I mined some bitcoin in the early days, when you could solo-mine for a week or so and net coins. I had a handful of coins that I cashed out for less than $100, because I didn't like Bitcoin as a long-term investment. If I'd sold half, I'd have made a tidy profit off the sale of the first half, with another handful of coins that, even if they tanked, I'm still in the black. But, if they go to some ridiculous number, like $10,000, I'm substantially better off.
Needless to say, I didn't save half, but even for people buying in now (I'm not), could end up doing well, even if the trajectory of BTC is $15k, $20k, $45k, $0, Of course, if the trajectory is $15k, $10k, $5k, $0, they'll be shit out of luck.
It's crazy to think an amateur investor in Bitcoin is going to be able to "keep the exits clear". By the time you see the downturn those exits are long gone.
If an amateur can actually guess when the downturn starts (a really big if), they should not have much of a problem exiting. Even if a large investor can identify the downturn, if they try to exit quickly, they will probably just exacerbate the problem, without even being able to get all the way out themselves
[1] Although some whale customers may be able to. They may win big - or at least, lose less, at your expense.