To be really good, you need to sell all at the precise top, and then buy it back at the absolute bottom.
I doubt anyone actually did.
Perfection is not possible, but getting closer to it is a noble and sensible quest.
My sense is that if you aspiring too much to get exactly right or too close to perfection, then you are being too greedy, and you are engaging in gambling and unrealistic chasing of windmills.
Better aspirations are likely to attempt to be practical when opening and closing positions, and perhaps structuring whatever you do in a way that you win no matter what.... that would be my understanding of a closer approximation of perfection that is not really gambling, but removing emotion and perhaps even removing some of the impossibilities of attempting prediction.
To be really good you just need to be better than the average trader. And for that you don't need to sell the exact top or buy the exact bottom. It's enough to stagger purchases and sales in proportions that depend on the probabilities of price increases/decreases by certain numbers. Finding the probabilities is the trick here, as well as averaging them out in a way that guarantees you a performance band in which your portfolio will fall with a given probability. Doing that requires an understanding of time series as well as the ability to process large amounts of data (beyond just the price charts) though.
Wowza!!!! Much better said that me.