I am going to talk about investing mistakes.
1) All in margin in one stock.
2) Diversification in just one sector.
3) Selling winners and holding losers.
4) Selling when there is blood in the streets and buying when everyone is happy. (Warren Buffet does the opposite and so far it has worked for him, however, he could have scaled out of some of his positions when everyone was happy instead of just holding them forever.)
5) Not owning any dividend paying stocks as part of investing. Dividend paying stocks is one of the true edges since they will help protect a stock during a bear market and continue to give you money even if the stock does not go up.
6) Not owning gold, oil, or platinum stocks when countries are devaluing their currencies. Also, if you think they are all too expensive to buy now, you would be wrong, some stocks are about to get their mines started and are trading below their net asset value.
7) If you see a big short position, you need to determine why, since the shorts are usually smart money. Only if you can determine they are wrong, will it be a good idea to go long in hopes of a short squeeze. The difference being a small float stock where many of the shorts are retail shorts and not smart money.
8) Not owning some dream stocks and holding a core position until they pay out. These are stocks that if everything goes right for the company they could go up 1,000% in value.
9) Staying on full margin as the market is crashing.
10) Buying stocks right after Cramer recommends them.
11) Buying a stock that ends in a .pk