Some use all their funds to start up and hoping to get something in return like a larger amount just to feel among, 75% of this crazy investment do not work for some but it does for some. When people sell BTC these are the cause, I'm saying this because they seem to forget that having a plan B is important in every investment.
And since they can't predict the next move of Bitcoin price it put them in a confused state and some can decide to withdraw something less than the start up amount let it be that they get something to hold on to, no need to blame those withdrawing because they don't have much patience.
This is why it is adviced to invest funds that you willing to loss to prevent emotional battles with market trend
DCA should be done. With spare money not full capital or money for emergency.
You can reduce your everyday expenses and set outside some for investment and another for emergency savings.
The amount a person uses for DCA varies based on their situations
Imo, going "all in" when investing in Bitcoin is not advisable doing such can cause mental breakdown and lead to selling in loss when there's need to use some of the funds or Bitcoin bears has finally gotten to the persons head.