It is? I'm not sure how you'd disprove it. Anecdotally (which I suppose actually matters in this case!) I've had a case where a (fairly long, 26 character) password I used regularly suddenly (and thus far, permanently!) went out of my head. I can remember some fragments of the password but not the whole thing.

The only novel issues encryption brings to the table involve self incrimination, because, AFAIK, IANAL, etc., the only time an encryption key is inarguably protected by the fifth amendment is where the fact that the defendant knows the key is itself incriminating evidence, because the fifth amendment only applies to self-incriminating testimony, not other self-incriminating evidence in the defendant's possession (e.g., the contents of a hard drive, encrypted or not).