Making The Writing Process Easier

Is struggle and frustration an essential part of the writing process? I can't think of a single writing project of mine which hasn't involved staring helplessly at a blank page. I can feel the words inside of me, but try as I might, I can't get them out. I am currently trying to write the conclusion of my PhD thesis, and struggling at it. I know the words will eventually come, I know it will go through a few or several revisions before I am happy with it. The same goes for my PhD thesis. It is not there yet, but it will be one day unless calamity strikes. It will give me the feeling of completeness and fulfilment that every writer aspires to with every writing project, big or small. So, why so much frustration with an unproductive session? Should I just do something else if the words are not coming today? Or, it the anguish any essential part of the writing process? Will the words not come if I haven't paid my dues in terms of  anguish and frustration. Is the anguish and frustration what propels my writing process forward? I don't know.