How do you gain confidence?.
You gain confidence by backtesting your strategy with historical data not to check the amount you can make out of the but the amount you can lose and consistency of your trading plan.
All these with other rules has helped me over this years become a more profitable trader than I was.
Without a doubt backtesting your strategy is key if you want to know if there is any chance for it to be successful, but you need to be careful as there are two mistakes that are incredibly common when backtesting a strategy, and those are overfitting and the look ahead bias.
It is very easy to make the former mistake as in our desire to improve our system we have the tendency to move the parameters of our indicators so it produces the best profits with the smaller amount of risks, however you are only fitting your strategy against the data, and when trading against the live markets it will fail.
And the look ahead bias can be even more difficult to eradicate, since you are using historical data this means that you already know what will happen before anything happens, so it is easy to tweak the system to anticipate those conditions and avoid making a big mistake or make a killing with a perfectly timed trade, something that will be impossible to do when you are trading the live markets.