Weaknesses of Contrarian Investing

It is a risky strategy, as it goes against the conventional wisdom of following the market direction.
There is relative information deficit regarding contrarian investment opportunities in the market, so much depends upon the assessment of the individual investor. If that goes wrong, the investment would not yield expected results.
There must be some cushion for short term depreciation of investment value while using the contrarian investing. For example, suppose some stock is trending up since long and the contrarian investor expects a trend reversal. So, he would short that stock at certain price level. It is possible that the trend reversal happens, but after price increases further from the price level the investor entered. In that case, the investment value will decrease and he may even get a margin call if there is no sufficient amount in his trading account.
The investor usually needs a long term investment horizon to earn a good rate of return.