I don't know why you felt the need to leave such a miserable and hateful comment on someone who obviously understands the subject matter of the video far more than you do, but you're being needlessly obtuse for no reason. This video isn't saying that you should plug your ears and say 'I'm happy' while you struggle in the real world, it's saying that you can take pleasure in the day to day progression towards your goals rather than putting it all at the end. If I want to lose weight, and I'm only concerned with having less weight at the end, I won't enjoy running. This isn't because the act of running is not enjoyable, but rather the perceived blockade in front of the goal, and the need to "get through it" to reach it. If you instead find happiness in the progress made by running, it is much easier to engage with it and keep up long term.
This method obviously isn't the catch all solution to your problems, and more traditional styles of reward systems are very beneficial when used correctly. However the way you speak seems to suggest that you believe that there can only be one or the other, which simply isn't the case. Your niece is still young, at a stage where self control and motivation aren't really the forefront of our brains, so in that case a traditional system would work better. For kids, doing schoolwork sucks, so getting a gold star for completing it is a good way at reinforcing that good behavior. But for someone older, when a goal can be months or years down the road, what good does putting the reward at the end do? Why not try framing your situation so that you may enjoy the progression towards that goal?
It is also quite baffling that you assume the people who don't enjoy the work are the ones that excel or are the fastest at it. I'd say the people who actually know the ins and outs of something and find joy in it are the ones that can more likely optimize and do the work better. I don't see many people at the top of their industry saying "Oh I didn't like the work but it was the absolute hatred I had of it that made me do it so well!" It's just simply not the case. Again not to say that you should necessarily be overjoyed in dumb work, but to completely disregard this method of framing for seemingly no other reason than you disagree with it is a very telling portrayal of your character.
Also don't say you're not an academic and then try and tell me about brain chemicals and runner's high, it just shows that you're willing to spout nonsense about a topic even when completely uneducated. Most athletes, let alone the general population, almost never experience runner's high. This is because it is only activated when the body is in need to return to homeostasis after a long sustained effort like a marathon, and endocannabinoids are produced to alleviate the pain caused by it. This means that most people who feel good after a run aren't feeling runner's high, but a form of progression based happiness shown in this video.
Don't go around belittling others for trying to live a happier life than you, especially when it's on a video you obviously clicked on because you deal with motivational trouble, and then decided was too hard to actually employ in your own damn life.