It's about staying up to date about new technologies and scientific insights/developments. Since my topic is only interesting to me (and I'm supposed to be up-to-date on the latest developments) I need to pick research that's interesting for everyone in the department, from clinician to statistician to biologist. That in itself is already impossible, reading up on all the background and delivering the message to such a broad audience while keeping the time-investment at the minimum definitely is a challenge.
I remember my first presentation in college very well, I was extremely nervous and thought my fellow-students would feel it was bad. Instead they gave compliments afterwards and said I looked so calm and collected, that's when I realized that it's ok to be nervous and you can deliver a good presentation regardless: as long as you take your time and not rush.
Sometimes I get a brain freeze that I don't have a clue what the data presented in a slide is supposed to say, but I always put the necessary information in the title so I just say that and hope nobody asks a question on the actual experiment