What is the most important thing have you ever learned?

I asked to my friends about it. What is the most important think have you ever learned. I want to share their answers;

"time, it passes how our elders told us, my university already finished."

"you must make the same mistake again and again because you will never learn your lesson!"

"saying lies is important"

"your intestine can control your brain."

"life is not fair. I was never equal to people. you have to obtain your own luck"

As you can see, everybody has a different answer. My answer is knowledge. I think learning more is the most important.
What do you guys think?