Investment horror stories

[Rodney Sums]

Dear experienced, and even newer multi unit investors:

If you could go back in time and give yourself advice, what advice would you give?  

If you knew then what you do now, what would you have done differently?

What choices have you made that didn't produce desired outcomes and became learning experiences?

What are some of your horror stories, and how did you overcome them?

I'm currently reading a couple commercial real estate books (one of which is a textbook) where the author speaks of some of their own experiences (for example, incorrectly verifying all owners of a MF he was trying to purchase thus being unable to sue for breach of contract when they backed out).  

I would love to learn from your experiences if you're not too proud to share!