It’s not as easy to not lie as many people here think. People being interviewed in these cases get asked an enormous amount of detailed questions about events which may have happened long ago, which they may easily misremember, and/or they may misunderstand the question, or respond awkwardly themselves. I suspect that if prosecutors deliberately set out to entrap someone on perjury charges, they can probably succeed close to 100% of the time.
This is just based on myself speaking to people about events which happened long ago, and the frequency with which they (or I 
) misremember small-but-significant details (and generally in a manner which is consistent with their overall take on the situation or their roles in it - which would be prime perjury stuff).
And that’s even without the stress of being interviewed by prosecutors and facing possible indictment yourself.
[A certain relative of mine was once interviewed by the feds (I think the FBI, but I’m not sure) who were investigating his boss for his suspected involvement in some criminal conspiracy (the boss was related to someone involved). My relative was a crucial alibi witness, because he was with the boss at a trade show when the crime went down. The investigators were gentle at first, and told him they understand why he would want to protect his boss etc., but took a harder turn as the conversation came to a close, and said if he was lying to protect his boss he would get in big trouble himself, and if he wanted to change his testimony he could still do it. But the real truth is that point it would have been too late. If he changed his testimony then he would be explicitly admitting to having lied in earlier parts of the interview, and he would be forced to testify to anything they told him to say, or be charged himself.]
By the way, jtur previously claimed to be an attorney, specifically in a class action suit . Surely an attorney would know – or could easily find – answers to such questions.
I’m pretty sure that “claim” was rhetorical. (His point was that the attorneys made more than the ostensible plaintiffs in class action lawsuits. Another poster said he was such a plaintiff so jtur posed as a hypothetical attorney in that case.)