Investors splurge at the free online stock trading buffet

When you give something away, people are likely to consume far too much of it. That's true of food, it's true of drink, and it's true of options trades.

Why it matters: The best thing that an investor can do is nothing. People who actively trade the market are effectively trying to time it — to buy low and sell high. Voluminous literature has shown that it just doesn't work, and that doing nothing is superior to doing something a significant majority of the time.

What's happening: Most online brokerages now charge $0 for stock trades. Even Vanguard charges $0 to trade in and out of stocks, ETFs, and, yes, options. In turn, hundreds of thousands of investors flocking to places like r/wallstreetbets are sending trading volumes through the roof.

Be smart: No good can come of this. The one silver lining to high stock-trading commissions was that they discouraged trading. And the one advantage that retail investors have over the pros is that they have the ability to buy and hold for the long term, without trying to outperform on a quarterly basis.

• If the market turmoil is tempting you to buy or sell, you may want to think again.