I just solo'd Angarvunde in the Rift, and that boss was rough for an adventurer character with no real specialization. I'm pretty damn proud of that. Made me think of other moments I was proud of completing, like soloing Rkhardahrk in Craglorn (also rough as hell). I'm curious about what moments other people have as their proudest in ESO, either because of determination or skill.
Try to stay away from luck-based things, like finding a rare drop first try. And remember that these things are subjective. I have no doubt that for some of you, the two examples I gave would be nothing, but it was hard for me and it made me feel good, so be nice.