"I should be doing something else, something more urgent."
"It's too difficult. I can't continue."
"I wonder how this piece sounds. I'll just play it once and come back to the one I'm practicing right now later."
"I think it's good enough. I should stop."
These thoughts will come to you again and again as you practice. It's inevitable. They are part of who you are. How you react to these distractions and excuses is a different story.
Sure, you can shut down your computer during the time of practice. Or you can practice only after a nice lunch. Or you can choose only the easy pieces, the ones you can almost sight-read.
Or you can learn to be aware of these distractions but ignore them. The feeling is sort of like looking at yourself from a distance.
Everyone of us has overcome them at least once and continued practicing with focus. Surely you can do it again.