Muse is weird

For weeks, I have not been able to make any headway with my fanfics on John Uskglass and Thomas of Dundale but suddenly, in two days, I suddenly wrote more than ̃̃̃̃seven thousands word and thus completed the first draft of it. And I also stayed up until 4 a.m and 2 a.m yesterday and tonight.

Why can muse not come at opportune time like Friday and Saturday, days when I canstay up late knowing that I don't have to wake up early tomorrow.