I fully concur with your view regarding positive motivation being a dominant factor in learning.
Many people have criticised Malcolm Gladwell’s pop psychology book Outliers for presenting a lop-sided view of the theory on what is required to become an expert. (Indeed, I haven’t seen his book mentioned once in any reading this week; it’s been so maligned!) The criticism is rightly deserved; Gladwell’s methodology is that of a sensationalist, point-making journalist, not that of a careful scholar. However, and this is the reason I mention him here, the famous 10,000-hour rule does contain one nugget of truth. Without motivation, no one is going to spend that many hours in a single discipline. I’m a firm believer in the 10,000-hour rule as a general heuristic for mastery, not for Gladwell’s reasons though, but for motivation/ interest reasons. It’s not a scientific theory, however.
Gladwell, M. (2008). Outliers: The story of success. UK: Hachette.