There are a number of different "day trading" strategies, some are easier and more reliable than others. Different strategies will work for different stocks, so it's really just a matter of getting to know the stock.

Big institutional traders are limited by risk, the fact that they are market makers for stocks in many cases, and the returns required need to be high, since their salaries are pretty ridiculous. Because of this, the fact that you're generally worse than them isn't a dealbreaker, just find a mid volume niche and learn it really well, then trade around general market volatility.