Is there any concept in the legal world that covers laws that are too difficult or impractical to comply with?
Here's an example; suppose an American moves to the UK and buys a house. The mortgage is for £300,000, which is equivalent to $300,000 at the time of purchase. However by the time the house is sold, 20 years later, the house is worth £900,000 and is equivalent to $1,200,000. The owner must now calculate exactly how much money he earned - taking into account the GBP/USD exchange rate every time there was a mortgage payment. This would require many dozens or possibly hundreds of hours to do, at massive cost (if performed by a tax professional).
In the example above, should the owner not properly follow these rules, and perhaps just make some rough estimate, could he be held criminally responsible for filing an incorrect tax return?
Or does there exist some kind of defense that complying with the law would simply have been completely unreasonable or impractical?