The big thing is that around 900k is when you get diminishing returns on savings vs market fluctuations. Bumping that amount by 10% would require saving $90k, which is a tall order. Or you could wait for a 10% market increase (it's up 14% this year). Not that the market is guaranteed to go up, or even by that much (we're in an unusually good market at the moment with inflated optimism). But at a certain point you hit a tradeoff where the market on average increases your wealth faster than savings off your salary will. At that point it makes sense to transition to a job that just covers your cost of living - one that you like more and offers more freedom.
At a former job we could not pay anywhere near top of the market and yet we attracted decent talent as the mission was something that resonated with many people. One category of people we'd attract were those who had already made enough money that they didn't have to focus on that, and now just wanted to do good in the world.
For me at least, the goal has been to bank big cash early, then let the compounding do the heavy lifting towards the end. As I mentioned above, getting a 10% increase takes a lot more savings late in the game whereas the snowballing effect of compounding interest is stronger, so I'm coming out ahead just by staying afloat without dipping into my savings. I look at the work that appeals to digital nomads (pre-covid, this was work FAANG and other high paying jobs didn't widely offer), and it seems more valuable to spend some mobile years financing a nice adventure with the stability of a job that lets me work from home. It means a gradual transition to RE and that very little in my lifestyle should change once I pull the trigger. Personally I'm looking to reach FI /then/ transition to a remote/part time job as a way to reduce risk while offering some extra flexibility - everything I earn in that time should be gravy and it should allow me the freedom to travel and enjoy the experiences.
Of course if you are retiring in your 40% you may want to be pretty conservative...
Retiring in 40s is a pretty big decision. It's not impossible to re-enter the professional workforce in your late-40s or 50s, if things don't work out, but it will almost certainly not be easy.
In the UK tax advantaged pension accounts cannot be accessed until you're 55 (and 58 for my generation)
https://www.financialplanningassociation.org/article/journal...
People in the FIRE communities are routinely discussing 3.5% and 3% SWR's, and see 4% as risky.