He might be able to take all the profit

Yeah well, the "profit" is only for the guys who just invested, older investors certainly aren't at a profit.
So they took the risks and aren't going to see most of the profits because the investment is now much higher.
Great.
If you divest when it's up a few k, and invest when it's down a few k, you will have higher returns than the average and make up your loss. This because when it is up a few k there are more investors and less to earn, whereas when it is down a few k there are less investors and hence more returns on your capital. Basically do the inverse of what the greedy/scared investor does.