This advice reminds me of an anecdote from Art and Fear [1]. A ceramics teacher divided his classes into two groups. One group he told would be judged only based on the quality of the best pot they made, the other group would be graded based only on the number of pots they made. After the two classes had finished, the teacher noticed that all of the highest qualities works came from the class that was aiming only for quantity. It seems, at least for artistic/creative activities, simply diving in and making lots of attempts is the key to rapid improvement.
If you follow the citation trail for that you end up with nothing, no individual who says they did that and had those results. The same anecdote shows up in the War of Art.
The same is true with photography. Take tonnes of photos, and some will be great. You begin to take on board what makes some photos better than others. It seems to raise the quality of all the photos. We're basically talking about focused practice, but applied to aesthetics.
[1]: https://www.goodreads.com/book/show/187633.Art_and_Fear?from...