I did it for a few years and I was averaging about €600 profit per week. I only dealt in 10 shares on the Ftse. Knew them inside out. All good companies. They all traded within some sort of pattern on a daily/weekly basis and around ex dividend dates. I bought when low and sold when high within a tight price range. Also did some short selling when high and bought back when low. Then I got bored and greedy and started trading some shares I hadn't studied properly and started trading on gut instinct rather than on fundamentals. Lost a big chunk, lost my nerve.
There are the people who get the news first. There are people who get the news second. There are people who get the news later in the day. There are people who get the news in the next day's newspapers or in the Sunday papers. I thought I was getting the news in the first batch but there were already layers of people who had bought and sold before me.