When a complaint is first file, per case law, courts have a duty to
believe each allegation you make on information and belief as long as
they are each not contradicting any other statement or other evidence
present at the time of filing.
This isn't true. The court doesn't have to actually believe you. The court merely has to assume for sake of argument that the things said are true for the narrow purpose of evaluating whether they describe a legal wrong in a formal sense.
Also, under modern federal pleading rules in the U.S., the judge doesn't have to believe you and can dismiss your complaint if it is not "plausible."
Your attorney has a duty to not merely assume that everything that a client tells the lawyer is true. In federal court, the governing rule is Federal Rule of Civil Procedure 11, which states that when an attorney files and signs a document in court that the attorney:
certifies that to the best of the person's knowledge, information, and
belief, formed after an inquiry reasonable under the
(1) it is not being presented for any improper purpose, such as to
harass, cause unnecessary delay, or needlessly increase the cost of
(2) the claims, defenses, and other legal contentions are warranted by
existing law or by a nonfrivolous argument for extending, modifying,
or reversing existing law or for establishing new law;
(3) the factual contentions have evidentiary support or, if
specifically so identified, will likely have evidentiary support after
a reasonable opportunity for further investigation or discovery; and
(4) the denials of factual contentions are warranted on the evidence
or, if specifically so identified, are reasonably based on belief or a
lack of information.
The California state law obligations is more or less identical in substance, although the procedural rules of California are codified differently than the federal rules.
So, a lawyer is required to reasonably inquire into whether the client is telling the lawyer the truth about the client's motives and about the facts. It is a breach of the lawyer's duties to the court and the profession to simply take what a client tells the lawyer at face value, accepting it uncritically.