Sell the losers and let the winners ride-It is human nature to make this mistake. Time and time again, investors take profits by selling their appreciated investments, but, in hopes of a rebound, hold onto stocks which have declined.

Most mutual funds don't perform-The truth is that over 70% of mutual funds fail to beat or meet market averages such as the S&P 500.

Don't try to "time the market"- Trying to detect when the market is going to move up or down isn't only hard, but impossible.

Waiting for the market to correct - Believing that the market is overvalued and waiting for stock prices to correct before investing will often get a long-term investor in trouble