1. PanicWhen people sell, they do it because they need cash or because it's too painful to sit on an investment that's going down. When people buy, they often do it because it's done well, even really well, recently and fear missing out. That's a perfect formula... for going broke or badly lagging the markets. The process is the opposite of what you need to do.2. "Hot tips"People hear, “This investment will make you rich. Fast, easy, and guaranteed.” Only the people selling crystal balls get rich.3. ProcrastinationAt 25: "I'm young, it's early, it's time to have fun and spend. Retirement is, like, 50 years away."At 35: "We have a young family. Finances are a bit tight this month. We have a big vacation coming up. Pretty soon we'll begin thinking about saving.At 45: “We needed the new boat and RV. Fun with the family, you know? Next year I’ll get serious about saving in my 401(k).” Next year turns into retirement and then it’s, “What the hell happened?”Don't forget the power of compounding. It's non-linear.If you invest $1,000 per month at 6% annual return for 40 years, that's $2 million.If you do the same but for only 20 years, that's only $450,000.You doubled the time, but came up with 4.44x the return.Don't start tomorrow, or next month, or next year. Start today.4. Being overly conservative“I just want to protect my principal. I don’t want to take any chances.” Cash is the worst thing you can have. The interest you earn is taxed and inflation more than eats up the rest of it. Yes, you should have some cash at all times. You should have an emergency fund. But in order to grow your money, you will need to take some risk. 5. Memory“I remember when a bank C.D. paid me 7% and I couldn’t lose any money.” That was 20+ years ago. Forward returns won't be like that. It is what it is.6. Gambling“You can’t lose money on . . . It’s the future. You just don’t understand.” Fill in the blank with dot-com stocks, bitcoin, houses. We all know the stocks right now that are like this or were in the recent past. Some might even be a fan of them. I’ve watched them all skyrocket. And blow up or later settle down to a fraction of their former bloated valuation.7. History “But this time it’s different.” The famous last words of an investor just about to implode. Spoken in euphoria or panic. Same result.8. Timing “I’ll get out now. Then I’ll get back in when everything looks okay.” I wouldn't try this. Forget the support and resistance and RSI and MACD. Nobody makes money with that stuff. Only broke retail traders think they do.9. Optimism “Investing is easy. I can do it myself. I’ll learn as I go.” Yep, you will learn as you go. Unless you run out of money first. It’s usually a lot cheaper to learn first or pay someone who has.10. Pessimism “I’ll never be wealthy. My dad wasn’t. My brother isn’t. My friends aren’t.” You can be. But no one has enough time to make all the mistakes himself.