for me:
Meeting the tyrant: Ignoring the warnings of my team mates, walking down the hallway by myself pretty far from the base, only to hear a roar that shook my screen and a giant dinosaur like thing hauling ass at me. I died.
becoming the tyrant: I was full of myself after 1-shotting all the unarmored humans, believing I was nearly invincible... but the thought that did not occur to me, was that if all the aliens on the team had the capability to become a tyrant, then the humans had to have a way to combat them. I became intimately aquainted with the lucifer cannon a few minutes later.
