Actually I think the advice does apply to mundane things like speeding tickets. If a cop pulls you over for speeding and asks "do you know how fast you were go

Actually I think the advice does apply to mundane things like speeding tickets. If a cop pulls you over for speeding and asks "do you know how fast you were going" if you are even thinking about contesting the ticket, many answers to this question would be a mistake. Fully exerting your rights might be a little antagonistic in this situation but you may also wish to give a complete non-answer, like "Yes, but I'm sure you're going to tell me." Even if you just think you're just a witness to a crime, they might think otherwise. I'd tell people to trust their judgment but prisons are filled with people who trusted their judgment and thought that talking was OK, so clearly that's not always enough.