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.