Numbers don’t tell everything. Outperformance is one period could be simply due to the fact that the market environment suited the stock portfolio. A fund true performance potential needs to be evaluated within the content of market environment during the different periods used.
As we known, market conditions change rapidly and frequently. A fund manager who is good in delivering strong returns in a particular type of market conditions may fail when market condition changes. As such, in fund selection, you need to understand how different types of market condition affect the performance of a fund.