What are your biggest investment regrets and what would you have done different now?

Just a begginer at investment here looking to learn some wisdom from fellow more experienced investors.

I've been educating myself specially on the internet and look forward to start reading some books as well.

It would be interesting to know some personal stories of hardships that I can learn from in advance.

I've understand that is important to keep being rational and sticking to a plan cause emotional investment often goes wrong.

Share whatever you want as long it was a mistake and you learned something from it. Any help is much appreciated, thanks!