What you paid for an investment. Holding on to a losing investment until you break even can burn you badly. Some stocks never come back. Buy and hold can work out well for some stocks, but for others, you're just throwing good money after bad.

The time and effort you put into your investments. Doing due diligence when choosing investments is crucial. But there are no extra points for effort in investing. How hard you worked on your analysis matters far less than how good a job you did.

How much you could have made if you would have only put $10k into… This sort of backward looking fantasies are useless, unless they teach you how to pick the next 10-bagger before it shoots up. Otherwise, you may as well throw darts at a list of stocks. Enron anybody?

Timing the market perfectly. Looking at market returns, for individual stocks, funds, sectors, or indexes, can be fun or terrifying, but not very useful. Nobody can consistently pick the best (or worst) times to invest.

Beating the market. Investing is about achieving your personal financial goals, not beating the market. Would you rather get great returns but fail to achieve your goals (e.g., because you invested too little, too late), or achieve your goals with mediocre returns (because you invested early, often, and consistently)?

Short-term performance numbers. Your short-term performance will be great some of the time and miserable other times. Who cares? Long-term returns are the only ones that matter.