Well, charting is basically trying to understand the people on the other end of the screen. Think of it like a poker game. Instead of reading their faces, you read the tape of the price movement, which is not random but rather the outcome of many behaviors.
Now, what has made charting perhaps even more useful is that a lot of people use charting! Meaning, I can look at a chart, see the signals like triangles, and then I know, every day trader sees that triangle too, and they are assigning meaning to it.
Meaning, most all traders now expect a volatile price swing, because charting exists. Charting is a self-fulfilling prophecy, except it gets manipulated and gamed heavily.
Just as an example, on Poloniex often large orders are placed in the feed to manipulate behaviors of the trollbox and the attitudes of people. Then just when that buy order is needed to support the market, it vanishes. Many traders will panic sell when it leaves too, and I have been there trading one day when one of those large manipulated buy orders vanished. Bitshares crashed within 15 minutes of it leaving. You get good enough at it, and sit in the chat daily, you'll begin to spot the fake buy walls that manipulate people but then vanish.