Bad experiences

"Bad experiences are often the most memorable." - M.C. Serna

I can't remember his full name, nor the exact quote, but he was my professor when studying my Master. It sounds like one of those silly things teachers say when you're having a bad time, but it has stuck with me. He gave my group a really hard assignment for the next day, and that's what he told us. I wonder if this happened to him in the same way, or why did he say that, but it was pretty accurate. We decided to spend the whole night working on the assignment. No sleep, just work... and pizza, and drinks, and music. We spent the whole night together working on that assignment, ended up really tired and sleepy, but it was a really memorable experience. 

When I look back, I have plenty of awful experiences that I can remember clearly, and sometimes… fondly. Why is it that even a bad experience, becomes a cherished one when we're looking back?

It’s like that scene from the movie Click. The protagonist realized his dog was dead and got really sad. He then remembered that the last time he saw his dog, it was trying to hump his leg and he didn't let him. "…And I should've let him and I'm sorry!"

Likewise, I scolded my little friend for eating my cookies. I knew full well that it didn't matter, but I scolded her anyway, trying to discipline her or whatever. What if I never see her again? Was it worth it?