My biggest distraction: Working at home. I have a student job at my university and work at home. Just visit my boss every other week to show him the results.
So I always thought it's amazing to work at home. No need to travel to the work space, I can arrange my time as I like, noone's constantly watching what I'm doing.
Sounds great, right? Yeah it is, but is it productive? Lol no.

I'm getting distracted by everything. New mail about some kickstarter stuff, one hour wasted. "Can you help me with that computer problem?" Yeah sure. "Wanna play some League of Legends with us?" Sure, but just one round, I need to work. Ten rounds later I wrote like three lines of code.

I could ignore all that stuff, but I'm at home and can do whatever I want, right?
Results in me working through all night, because then there's noone to distract me.