Quoting Casey Handmer’s blog:

Where do you get your dopamine? This would appear to contradict the earlier points about finding the toughness to do hard things. But it doesn’t really! It is always easier to learn things you enjoy doing. The art lies in finding ways to enjoy the things that are necessary, even if you have to approach it abstractly as Type 2 fun. And finding ways to avoid enjoying to excess things that are counterproductive to your mission in life – usually addiction in various forms.