hard things should motivate you, easy is boring.
There is such a thing as too hard though. I tend to dig in on something hard and then find out it's too much to do consistently, day after day. In that case, I can just ease back and have plenty of material and plans.
Yes, I've had that happen to me a lot. Now I have a lot of plans and don't know how to start usually. But piano is infinitely easier than ear training. At least there's progress, memorizing a bit better, learning something even if it's just a note a day. Piano is at least POSSIBLE, unless your hand is too small, or you don't have hands at all. But hearing? How do you know you're hearing something correctly? It's all just guesswork to me.
Other studies are like that, you don't understand something, or there's a gap in your knowledge, you're stuck there, maybe forever even. We're so lucky to have piano. It's not easy at all, but at least fulfilling in that sense.