Many people loose money by investing in stock markets and then they curse the markets.
So a suggestion is invest sensibly. Invest Smartly !

Here are few common mistake which people make.

• No proper planning.
• Aggressive Buying without knowledge about the company.
• Aggressive Trading.
• People keep on Trading in fact over trading.
• No balance between various kinds of Investments.
• Not Investing for long Term.
• Speculative Trader.
• Sell even when a minor uptrend is seen.
• Taking loans to invest in Stocks.
• Borrowing money from Friends and Relatives.
  
• Only depended on Analyst views.
• Follow Tips what others give and not putting your own value inputs.
• Depending on an unreliable person for help.
• Investing full amount in Penny Stocks.

Among these the most common once are Depending on Tips by Analyst , Aggressive Trading and Investing in Penny Stocks.
During bull run we saw that people took loans for investing keep their house property as mortgage and lost a huge sum of money. Few people also borrowed money from Friends and Relatives.

Related reading : Common mistakes made while investing in stock markets