If the time horizon of your investments is short (a minute, an hour, a day, a week), then you become part of a crowd of billions of people trading on the stock market. Some of them lose money, some make money. In order to earn not just once, but more or less consistently, you need to learn how to outperform at least half of these billions of your competitors. After all, money and securities simply move from one pair of hands to another within this crowd.
On average, stock prices in the U.S. market grow by 4–7% per year in real terms (after inflation). This is primarily due to the fact that issuing companies consistently generate profits, grow, and become wealthier. Why not become a co-owner of the best companies, hold their shares for the long term, and participate in this growth of wealth?