This is the Strategy I was following in crypto. This is the example.

buy coin 300A @1.00 = 300

Sell 150 @2.00 (Now you covered your initial investment(Excluding fee))
Sell 50 @3.00 = 150
Sell 50 @4.00 = 200
Keep remaining 50 for long term( If market is crashing you have to sell this proton immediately).

But this method can't apply if the market crash before it reaching to 2x. I would like to know the approaches/Strategies you are following and drawbacks of this method.