blueyes

This whole question revolves around the effort/reward ratio of a behavior. When people talk about ~21 days, they're talking about doing a hard thing until it's second nature and seems easy.

But there are other ways to make something seem easy, and there is another component in the ratio: reward. That is, even if effort stays the same, you can wire a habit by making the behavior more rewarding. (This is why people are able to get addicted to a substance after one dose -- because they can't forget the state they entered ... and it was so easy to get there.)

So the takeaway here is the you can wire habits by decreasing the amount of effort to do something that you think is good for you -- eg if you want to hydrate more, place a glass near the sink so you drink water when you get out of bed in the morning -- *and* by increasing the reward. The whole trick is getting the ratio right.

Cliche Silicon Valley example. I did an ice plunge, and it gave me a day long plunger's high. I didn't need to plunge for 21 days to get the habit. I started doing it 3 times a week after that, because I knew what I had to do to feel good.

This actually gets to something Huberman calls "duration-path-outcome". Getting clarity on what you have to do (path); how long it will take (duration); and what the payoff is (outcome), can do wonders for motivation. Confusion kills action (and for that matter, all deals, since habits are just deals we make with ourselves). If you can get clarity, reduce the effort, and increase the amount of reward and your confidence in it, I think you can get to new habits really quickly.

Focus = Energy - Distraction

and

Success = Focus x Time

The way you gain stamina is by doing things to increase your energy and decrease distraction. I wrote and talked about this here, fwiw.