Only when we sat down with spreadsheets, last year's return and my W2s did I realize that the grant money I received last year is income earned for, at least because of, my novel Judith.  It came out to about a third of my income for the year, maybe more.  
Because I wrote a big chunk of fiction, though it isn't complete yet.  Still have to do the research trip.  Still, as the accountant said, "You need to frame a copy of that W2!"  
I went into the meeting knowing that this kind of fact and number based work is vital to my life as a writer, ghostwriter and editor.  I never expected to weep tears of joy in the middle of all the grunt work!