One sure way to wind up in jail is to lie to the FBI. Answering a specific question with a definite "yes" or "no" when they know the opposite is true will put you in the slammer under Section 1001 of Title 18 of the US Code. So, one of the ways to avoid running afoul of that law is to simply say "I don't remember" or "I can't recall"; making it impossible for the FBI to catch you in a lie. That is, unless, you are already on record as having clearly shown you did recall or did remember.
It is interesting then, that when the FBI released their notes on Hillary Clinton's interview with agents regarding her email server, Hillary used the "can't remember/can't recall" tactic 39 times. Here's a women that specifically recalled talking to Colin Powell about private emails, and receiving an email from him over the issue, but can't seem to recall if she was ever briefed on how to handle classified documents.
CNN: FBI releases Hillary Clinton email report: http://www.cnn.com/2016/09/02/politics/hillary-clinton-fbi-interview-notes/
How to Avoid Jail Time for Lying to the Government: http://www.criminal-law-lawyer-source.com/tips/avoiding-jail-time.html
Hillary Clinton Told FBI Colin Powell Advised Her to Use Private Email: http://www.nytimes.com/2016/08/19/us/politics/hillary-clinton-told-fbi-colin-powell-advised-her-to-use-private-email.html?_r=0