Investing Principle 3: Stay Disciplined Over the Long Haul

It is essential to stick to your strategy for the long term. Even the best strategies have down periods, and it can sometimes take over a year to reap the benefits of a good method. If you try to time your use of a strategy, you'll likely miss out on some big gains.

Expectations shape reactions: be prepared for short-term 10 to 20% downturns that are inevitable in the stock market - and the less frequent but also inevitable 35 to 50% downturns you'll occasionally experience. You can't predict when they will happen, so you just have to roll with them if you want to reap the market's long-term benefits.

Give the Internet a rest. Checking your portfolio every day, let alone every 10 minutes, can make you want to jump in and out of the market, which hurts your long-term performance.