Trials and hearings before a judge aren't random, but they aren't terribly predictable either. The best empirical studies of high stakes felony jury trials suggest that the accuracy of a jury in a case that doesn't plea bargain is about 90%. They are right 90% of the time and wrong 10% of the time. The appeal process involving multiple instances exists primarily to correct these errors. If the first trial is 90% accurate and larger, more experienced panels are more likely to get it right, the likelihood of a correct result in 2-3 tries becomes more acceptable. (Easy cases settle.)
Bench trials (i.e. trials to a single trial court judge in common law systems) are just as final and probably not more or less accurate on average, but trade a more experienced fact finder who understands the process for the disadvantages of having only a single perspective on the facts from someone who doesn't have to persuade anyone else that he or she is right.
The appellate process in civil law systems is quite different and more likely to change the result than it is in common law systems, largely due to two factors: the need to preserve the jury trial right in common law systems and a much smaller number of judges in common law systems. Common law systems strive towards a get it right the first time or bust in one big event model, civil law systems creep towards a correct result bit by bit. Until the 1890s in the U.S., in federal criminal jury trials (and many state criminal trials), there were no direct appeals at all, only the equivalent of modern habeas corpus petitions.
Civil Law System Instances
In civil law systems, a first instance judges will take testimony and documentary evidence and argument in a series of hearings (not necessarily in one continuous compact trial), recording the testimony with personal notes rather than a verbatim transcript, and applying law to fact on a piecemeal basis that narrows the scope of the proceeding as evidence and argument trickles in. This results in a court order which will become a final order unless appealed. In "small" case the first instance court may be one judge, in a more serious one it might be three judges. The first instance court looks primarily to statutes and legal treatises for legal guidance with case law precedents taking only a secondary role that is not strictly binding. Because testimony is delivered to a judge, there are few if any rules of evidence.
There is not a great analogy to this phase in most civil procedure systems today, but it is a lot like a preliminary hearing in a criminal case or a preliminary injunction hearing in a case where injunctive relief is the main remedy sought at trial, or a traverse of an attachment in a common law court system.
If either party thinks that there were serious errors of law or fact in the first instance judge's ruling that change the outcome, they can appeal the case to second instance court where hears any issues upon which there is an alleged error of law or fact de novo before a new, more senior and more numerous panel of judges (typically two more judges than in the first instance court).
The availability of de novo review in a second instance court makes trial preparation in the first instance court much less expensive than trial preparation in the U.S. or U.K. where any factual error in the first instance court is almost impossible to overturn on appeal and where there is no time to regroup if you are surprised in the first instance trial. So does the fact that in a civil law system you may be preparing for only a few witnesses at a time, rather than all of the witnesses and evidence back to back at once.
Since most of the time the court correctly understands the evidence and there are no big surprises, and since the court narrows the issues over the course of the proceeding by applying law to each new set of facts, the amount of effort going into trial preparation and presenting evidence overall in a civil law system is often considerably less than in a common law system and these savings can often make up for more common and more time consuming appeals in civil law systems at the second instance.
In a civil law system, if the first instance court rules against you, but gets the case 90% right the first time around and no surprises come up in the trial, then you can proceed to a much narrower case in the second instance to get the 10% that the court got wrong the first time corrected without so many distractions and you have already seen your opponent's entire case, rather than having suffered an impossible to remedy fail.
A second instance trial in a civil law system is somewhat analogous to a first trial following some motion practice that resolved many of the pending issues on dispositive motions in a common law system.
Like the first instance court, the second instance court looks primarily to statutes and legal treatises for legal guidance with case law precedents taking only a secondary role that is not strictly binding except some rulings from the highest court.
A third instance appeal in a civil law system is more or less comparable to a direct appeal in a common law system, where appellate issues are largely confined to disputes of law and the facts found by the second instance court (as well as the first instance court findings that were not disturbed on appeal to the second instance court) are taken as established (again, usually without a verbatim transcript based upon a written order of the second instance panel). This court often called a court of cassation (i.e. of ending a dispute) resolves disputed issues of law. Typically, a court of cassation or supreme court will have dozens or scores of judges who have subject matter specialties and hear cases only in smaller panels.
None of these courts has a power of judicial review, which is typically reserved for a constitutional court that is a separate small panel court not made up only of career judges.
In a civil law system, if the judge is found to have abused his or her discretion in the original trial in a manner that requires a retrial, another judge rehears the case.
Common Law System Appeals
In the common law civil litigation process very few issues can be resolved prior to trial unless the relevant facts are undisputed and often not even then if substantial discretion is involved in a final decision.
In contrast, in a common law system, a single judge (often sitting with a jury of six to twelve jurors) decide facts in a trial from which a verbatim transcript is taken and reaches a verdict that can only be appealed if there is no evidence in the transcript and submitted exhibits that support a conclusion, or if there was a mistake of law or procedure (especially admission of evidence) in the proceedings that could have materially changed the outcome if decided correctly. There is no means by which factual errors or failure to respond to surprises can be remedied so preparation must consider every possibility no matter how remote. The trial is conducted all at once, typically in one to ten consecutive business days and all witnesses in the case must testify one after the other at this time. At trial, the judge carefully regulates what evidence is and is not permitted to be presented and instructs the jury regarding the law to apply to the facts and the issues for the jury to decide in its verdict. The trial verdict is final once the jury renders its verdict and appellate type issues raised with the original trial judge are rejected (or a retrial is granted on grounds similar to those upon which an appeal could be granted if a judge acknowledges making a serious mistake).
If either side thinks that there was an error, there is a right to a direct appeal to a panel of three judges that considers only the verbatim transcript of the trial, the exhibits admitted into evidence at trial, and legal arguments (typically no more than about three or four per party bringing an appeal). If the court of appeals panel on direct appeal finds an error of law or an abuse of discretion or a factual finding not supported by any evidence in the transcript and admitted exhibits, it will reverse the trial court, otherwise it will affirm. Jury verdicts are quite hard to overturn on appeal because they are upheld if any non-crazy jury could have reached that result even if they probably just screwed up.
In common law countries there are usually one or two more appeal available after a direct appeal (to a state supreme court and the U.S. Supreme Court in some cases), which strictly in the discretion of the state or U.S. Supreme Court with only a small percentage of cases even considered on this further appeal, and usually with just one or two novel or controversial issues of law raised at this point. Again, no new facts can be introduced or corrected on appeal.
In common law countries, if a trial court decision is overturned, the new trial will almost always be remanded to the same judge, even if the original trial verdict is overturned because the original judge abused his or her discretion in the original trial.