This article explains so much about my life, and about my day yesterday. To sum up, paying attention to what you're doing is tiring. The more things you have to carefully control or pay attention to, the less capacity you have for the rest of it. So if you're focused on learning a new program, that's way harder than using the same program you always use, and it may come out with you snapping at your coworker over someone leaving a paper jam in the printer. I know for myself, when I'm seriously concentrating on losing weight and eating less, I get much more testy about... everything, frequently coming to the conclusion that now is not the time for this because I need my patience for other things. So it goes.