Its difficult to say but I love when you spend ages working on a piece of computer code and it does exactly what you wanted it to do! When it works it can save you hours of time by speeding up your analysis.
I like the lonely and the social parts of my work as well. I enjoy spending long hours trying to figure out something myself, and I also enjoy having lively discussions and brainstorming with my colleagues and students. It is absolutely amazing that in my work I can collaborate with brilliant minds from all across the world.