Some people try to cleverly figure out what to say to each person about each situation, coming up with different lies and half-truths. Sometimes that works well for them, sometimes it blows up in their face. It's a bit of a crap shoot.
Other people figure honesty is the best *policy*, a long-term principle you stick to in almost all situations, knowing that in the long term, it works well. *Being* a liar doesn't work as well as being an honest person, they figure (and they're not wrong).
In my particular case, I have two additional reasons to *try* to be honest all the time. One, I tend to do things in the extreme. If I decide to be a liar and a thief, I'm probably going to be a big fat liar and steal well over the felony threshold. Secondly, my career is in security. 40 hours a week, I show banks and other institutions how hackers can exploit theirb systems. I study multi-million dollar hacks and thefts, because that's my job. I *know* how to steal a million dollars, I *tend* to go big in everything I do - if I decide to become a thief I might well end up in Leavenworth, not in county jail.