I can't find the article but I remember reading at some point about how difficulty of work relates to one's ability to get in the zone. To achieve some level of

I can't find the article but I remember reading at some point about how difficulty of work relates to one's ability to get in the zone. To achieve some level of flow, the work you are doing must be difficult enough to provide some sort of challenge and mental stimulation, while not being too difficult that you find yourself getting stuck and frustrated. So if you're not constantly trying to push your abilities to their limit, you're not going to find that sweet spot.