In the day of curated internet content, I think our most frequently encountered biases are the bandwagon effect (thinking something is right or doing it because everyone else is), the availability heuristic (thinking something happens a lot because we can easily think of examples), and confirmation bias (thinking information that confirms our beliefs is "more correct" than information that contradicts them).
Learning! Infographic on cognitive biases
I love cognitive biases! Okay, they're not actually great, because they lead us to often do the wrong (or less ideal) thing, but they are fascinating. Talking about cognitive biases is probably one of the number one things that makes me come across as a total know-it-all, but I can't help it! They explain why we so often do such ridiculous things and think we are right to do them. There is actually no way to counteract cognitive biases except (maybe) for being aware of them and noticing when they are happening.