Jerry Seinfeld has a writing routine in which he sets aside a certain fixed amount of time during which he can do nothing else but write.

It is acceptable if he doesn't end up writing anything at all during this session. But it isn't acceptable for him to do anything else during this time. This means no checking his phone, answering calls, reading an article, listening to music (or a podcast), talking to someone, going for a walk. 

It's almost like detention in school where he can't leave his desk or do anything else but the task at hand. His only choices are to write or do nothing.

This is quite similar to the time block technique that Cal Newport evangelises. 

This isn't just applicable to writing, of course. But to any kind of work that requires us to focus and create something - from music to sales presentations.

If you're struggling to do something, set aside a time and allow yourself to do nothing else during that time.