I think that a single stock or a portfolio is riskier (than the index of stocks) and it involves considerable time and effort (as well as money) to keep track of it. Can I beat the market with my...

I think that a single stock or a portfolio is riskier (than the index of stocks) and it involves considerable time and effort (as well as money) to keep track of it. Can I beat the market with my stock portfolio? Besides, how do I know that I have picked the right (i.e., undervalued) stocks in my homemade portfolio?