I find a lot of it for me is mental. Last year I did four centuries and some with much less of a base than others. I believe the last one I did not have nearly the miles of the others (maybe 200 in the month before) but had one of the better times and it was the hilliest. For me telling myself to enjoy the ride and doing it helps. Telling myself it is no big deal since I already have one that year works for me.