That's not to say that price charts and technical indicators aren't useful. It's just that being overly reliant on them can give you a false sense of your own predictive abilities. One of the best ways to prove this to yourself is to repeat the above exercise on a demo account.
Develop your theory based on past data, and then apply it to the current price action without second-guessing yourself or modifying your strategy. Doing this will prove to you how a strategy that seems to work when you fit it over historical data can quickly come unstuck when faced with real price action. Try it out and see for yourselves.