Mutual funds use economies of scale to invest in securities and enjoy returns that you might not be able to achieve on your own. Mutual funds are managed by professionals with experience, knowledge and access to the necessary tools that are needed to be able to pick securities that will bring better results that a single person could achieve.
This does not mean that you can not outperform a mutual fund. It just means that you a mutual fund will outperform a single individual’s portfolio most of the times.