There was an article on HN sometime ago about the practices of some old tribe to choose where to sow the crops for the next year. The practices were totally random, like watching the clouds, where a bird would fly, etc. Well, researchers eventually realized that those practices actually ensured a truly random selection and that was the best strategy. A non random selection, that is any possible bias, could have exposed the tribe to the possibility of a negative bias in selecting terrains and the risk of multiple years of bad crops which would have led to extinction. A random strategy would led to a bad year here and there and offer better chances of survival. But humans cannot make decisions truly randomly so they need a rationale system that helps them make random decisions. We are not that different from computers in this respect, but I am going astray now, so back to topic.
The markets are full of people trading based on their emotions. A stock is going up, greed and fear of missing out kick in and people buy high. A stock is going down, panic and fear of losing kick in and people sell low. People are psychologically wired to make bad decisions in the stock market, they have a negative bias. If you can find a rationale system to follow you will make better decisions than the crowd following their emotions and take their money.
Traders know very well that the first rule in the market is that everything can happen. They also know well that for any chart there are TA "rules" that say buy and other that say sells. They also know that a method will beat the guy with no method.
This at least is my theory, I have never practiced TA but I saw my father throw away tons of money with it and invariably the losses were caused by a few trades where he did not follow his rules but convinced himself to bend them a little. And he preached all the time that following the rules was the only way to win.
You are your worse enemy in the markets.