The worst horror stories - help us all learn what you've learned

[Ritch Bonisa]

I'm lucky, I get to talk to investors all around the world.  I learn something new on a daily basis.  I'm thankful for that.  I also understand that we don't learn anything unless someone else learned the hard way.  

I'm asking for some of those instances when you learned - "the hard way".  Please share a horror story if you can, but also please share what you learned from it.  This can be very helpful to newer investors and I think everyone who comes here wants to connect and learn something new.  

Keep it short if possible - and Thanks for your participation!