My list building mistake

What was my list building mistake? Sending leads directly and not making one.

To have sent thousands and thousands of paid customers as a super affiliate for some programs, and never collecting those high value leads myself, by giving them useful bonus offers. It's incredible how much money you can loose when you forget a single important step. A few years ago I realized what I was missing but even so I didn't reacted right away, the usual procrastination problem. I don't regret that time because that has no purpose, but I do learn with my mistakes...