What can one learn from their mistakes?

@Tazzie....this one's difficult for me because I knew better when I made this terrible mistake. So I don't see any silverlining. But what can I do so that this type of mistake doesn't happen again? What can I learn from my stupidity?

I need to speakup, make my voice and opinion heard, stayed determined and steadfast to my ideas when it comes to big fiancial decisions and don't allow myself to be emotionally manipulated by ANYONE!