Smaller moves, easier to obtain - A change in price results from imbalance of buying and selling powers. Most of the time within a day, prices stay stable, moving within a small range. This means neither buying nor selling power control the situation. There are only a few times which price moves towards one direction, i.e. either buying or selling power controls the situation. It requires bigger imbalances for bigger price changes. It is what scalpers look for - capturing smaller moves which happen most of the time, as opposed to larger ones.
Assess how much capital you're willing to risk on each trade. Many successful day traders risk less than 1% to 2% of their account per trade. If you have a $40,000 trading account and are willing to risk 0.5% of your capital on each trade, your maximum loss per trade is $200 (0.005 x $40,000). Set aside a surplus amount of funds you can trade with and you're prepared to lose. Remember, it may or may not happen.