As a small investor, your trading cost is just your personal computer and a chair in front of it, plus the transaction fees for each trade, which if you shop around, you can find $7.95 per trade or even $0 per trade brokerage firms. In other words, your total costs are entirely under your control.
But not for professional money managers - they need to have a posh office with fancy furniture at an expensive prime office building. They need to have receptionists along with a research team who will have to fly globally visiting companies. They have to print out nicely put together investor reports and pitch books and spend marketing dollars to attract new investors ...
In short, you can keep your costs low, and the pros can't. Are you utilizing your low cost structure fully, or are envy of the professional firms' higher cost structures?
In short, as a small investor, while you are disadvantaged against professional money managers, you do hold great advantages over them on Size, Time, and Costs! It's up to you how to play your advantage and win over those pros!