Nobody's answered this, perhaps because it's too obvious? Ooops, somebody beat me to it as I was writing!
Anyway, here's my bit, for what it's worth.
How can you 'do what you think is right at the time' without some sensible basis on which to make that judgement? That sensible, tested and proven basis is the necessary strategy. Otherwise, it's a guess and guess will lose you money. Yes, it's 50:50 up or down but it's the oscillations that will knock out the inexperienced, so you can't just guess and bung in a larger limit than stop.
Even when you've got the direction right, the chances are you'll still lose because the market won't go there in a straight line. What drawdown will you accept before you conclude you were wrong? Maybe you get a decent profit in the first 10 minutes but what is a decent profit - perhaps if you hang on for more it will reverse and go into negative territory big time. Perhaps it has much further to go and you close too early.
There's a hundred things that will kill you and without a good strategy to give yourself rules to follow, rather than making emotional decisions, you will most certainly lose money and never succeed.
Unless you are clairvoyant, in which case just pick the lottery numbers.
