If you enjoy an activity, you have an intrinsic motivation to do it. Once people give you extrinsic motivations to do it, and then take away those motivations, your inherent intrinsic motivation drops.
So if you like doing a puzzle, and then later get rewarded (e.g. paid) to do it, then once the payments stop, you are less willing to do it for pure pleasure.
Some people enjoy learning. Then school imposes extrinsic motivators (grades, etc). This can kill the intrinsic motivation.
Extrinsic motivators undermine intrinsic motivators.
A fixed mindset (as opposed to a growth one) results in a lower intrinsic motivation when you don’t do well.
Fixed mindset people fixed on grades.