Even when you are right, there are costs and taxes associated with being tactical. When you are wrong, there are opportunity costs.

In the investment business, you must expect to be wrong.

If you are not making any mistakes, you are being excessively risk-averse. Investing involves risk, and that means you will occasionally be wrong. And although it is okay to be wrong, it is not okay to stay wrong.

Commissions add up, taxes are a big drag, margin ain't cheap. A good accountant costs money as well. The math on this one is obvious, yet investors often fail to recognize it: Keep your costs low and your turnover lower, and you will win in the end.

When you buy anything with lots of leverage, it does not require a whole lot to go wrong to lose it all.

The simple reality of life is that everyone is wrong on a regular basis. By confronting these inevitable errors, you allow yourself to make corrections before it is too late.