'Pretend you're someone that can X' works for all kinds of things, not just challenging tasks.
People on the subway grating on my nerves? I pretend I'm someone patient. Need to bang out a particularly annoying task? I pretend I'm someone who's really interested in that task. Wife irritated by my sloth about the house? I pretend I'm someone who cleans up promptly. Feeling particularly miserable today? I pretend I'm someone who's naturally happy.
It doesn't work forever, and it doesn't work perfectly, but it works better than any other mental trick I've discovered.
It might be a trick but if done over and over, can't it have a bad effect mentally over time? I can imagine it can suppress your real emotions which can lead to a mental breakdown when you can't suppress them any longer.