<i>I understand the implications and everything</i>
I don't think you do.
<i>I can always say "I forgot[...]" Then what happens? I go to jail for 4 months?</i>
No, you go to jail for a few months and then they take you back to court to see if your memory has improved. If you don't have the key or if you produce a key that doesn't reveal the data they wanted it to, you go back to jail for longer.
If you can't produce the data the state demands, either because it isn't there or never existed, or because you really forgot, then you can stay in jail the rest of your life.
That is the purpose, goal, and implication that so-called law enforcement wished for and got from data investigation rules.
I said realistically. From what I've seen this "lost my password" is in the US a non issue, and in the UK it warrants a few months of jail time (treated as a misdemeanor depending on the severity of the charges). In any case, it's almost impossible to prove intent in cases like this. It can't be treated as obstruction of justice because the drives were not encrypted after the fact. And intent can't be proven, so at max you get a misdemeanor charge, fines and a year in jail (using us law as a basis for time served).
I'm pretty sure that there is a limit to the amount of time you can spend in jail for that (only a few months), at least for criminal cases.
I remember reading about a guy who was basically given an indefinite jail sentence in a civil case because the judge didn't believe that he really lost all his money is poor investments.
However I remember that the article highlighted the distinction between criminal and civil cases.
I don't think you do.
<i>I can always say "I forgot[...]" Then what happens? I go to jail for 4 months?</i>
No, you go to jail for a few months and then they take you back to court to see if your memory has improved. If you don't have the key or if you produce a key that doesn't reveal the data they wanted it to, you go back to jail for longer.
If you can't produce the data the state demands, either because it isn't there or never existed, or because you really forgot, then you can stay in jail the rest of your life.
That is the purpose, goal, and implication that so-called law enforcement wished for and got from data investigation rules.