You can't. Skill challenges are randomly thrown at you depending on what skills your Sim knows. I'd suggest dropping piano completely and not playing it again if you're not doing that already. There may be a link between what ops are offered and what your Sim is currently engaged in.
Exactly. I believe I had mentioned this before, but you (Blanchflower) could have overread it. The problem with the four instruments is that the last one will be the hardest because of other skill opportunities will come up also. That's what I was afraid of while trying, and that was what happens unfortunately.
The thing I can add to Metro's post is because I have put so many time in completing all the instrument challenges that I can say that giving only attention to one instrument at the time WILL let the game pop up more challenges in that particular skill. It's not 'There may be a link between what ops are offered and what your Sim is currently engaged in', no: there IS a link between those.
And to add more to that: playing at a party (thrown by yourself) at a park or so will force to pop up those opportunities even more. I have played simweeks and simweeks while my Sim was living for ever and the town pops up generations after generations and everytime I saw that playing piano at a party will pop up piano skills that day, or the next day.
More need to test this? I don't see why. How many times do you have to play to get 100% accuracy: 1000 times, 10.000 times, 1 million maybe? I saw this with my very own eyes, so I am convinced now that trickling music skills opportunities will work this way. If anyone still doubt it: just try out yourself. I just hope you will like repeating the same thing over and over again in the game. Haha!
