I regret it every time I see a mate's portfolio that contains some rockets I missed out on and could've jumped in with him.
But then again... you win some, you get the picture

The Germans have a saying on this:
"Wenn das Wörtchen 'wenn' nicht wär, wär mein Vater Millionär"
That means as much as:
"If the word if wouldn't exist, my dad would be a millionaire"