I guess my first “eureka” moment was when I was a student and we were searching for genes that allow a zebrafish to change colour. I found some fragments of a gene that looked promising and then “mapped” it to the genome. I found these fragments mapped to a location that is conserved all the way up through evolution to mice and humans. The same position in thoses species contained a known gene that is involved in skin and hair colour. That confirmation made me realize I had found the right gene in the fish and that I was the only person in the world, ever, who knew it.
It was very exciting, but of course the first thing I did was tell everyone else in the lab!