I know I have had to learn the hard way many times. It's easy to make mistakes in this hobby. I'll share a few later today.
My absolute worst mistake that I sadly keep repeating is to lay down my money while I am freshly lusting over the coin. It's like getting married during your first date.... I have the hardest time stepping back for a minute and studying before I lay my money down and whisk my newest mistake off to a life of loneliness in the dark recesses of my safe.
Buying duplicates of stuff I think I need to complete a series (because I didn't carry a list with me) but already have....
Been there, done that, got the tee shirt and all that nonsense. Believe it or not I did it twice just last week. That's a record even for a dummy like me. Bruce