The historical growth rate is 12%. You should stay invested for a period of more than 5 years to see returns like these.
Mutual Funds tend to do well if the companies they hold do well. Since equity Mutual Funds own ‘shares’ of some of the leading companies, the growth in the value of these mutual funds is linked to the growth in revenues and profits of these companies. Obviously, there is little more to it, but one can leave it to the professionals to manage that.