Always talk to strangers
We were always told to never talk to strangers. Everyone said so. But no-one ever could explain why exactly that was such a bad idea.
Instead of gladly accepting the predicate, I tried to figure out why. After some young reasoning I figured what they meant was something more like: be better at judging the intention of those you speak with, not all have the same intention as you.
This allowed me to be a little bit more suspicious, but not deny myself the chance of speaking to strangers.
Talking to strangers is one of the most rewarding things in the world. Just being let into someones world for two minutes can broaden your own horizons by many degrees. Sometimes you even discover new horizons!