When I managed to minimize the processing time of the project I'm currently handling. It went down from 30min-1hr to 7min-15mins. The project owner was so happy, said it made his life easier. I was told I did a good job by my manager.

I feel like a real dev then and there. So whenever I'm having a bad day, feeling insecure, I try to remember that day when I was able to do something right. :)