Annette was well prepared for the “project that never ends” by her years of cello lessons starting when she was two. The nature of musical proficiency makes your skill always a work in progress even if you’re a virtuoso.
So she was used to the idea that there’s always something more to do, and maybe this helped her to accept the necessity of giving up her Timetables of History project. She could have continued it, like an adult might clean out the closets in a mansion, knowing that the scope of the task requires persistence with little chance of completion. But since she already knew from cello playing that progress is valuable, even if you don’t get a final perfect product, she could let go and feel all right about it.