This is wrong, not always. Investors do have a bigger chance to make profit if they can hold for long term, if you can hold for 5+ years then yeah it would be easy to make some profit.

However, if you are not careful then you are going to end up with a lot more loss when it goes down and if you fear and sell, so there are investors, who hold for a year or even two, and then sell and make a loss, so be careful and don't be like them. On the other hand, if you are not careful then you could end up with trading and do the same, you could make a loss or make a profit, either is quite possible and can make you rich or poor. Always make sure that you are going to end up with right set of mind, and not focus on "how" it would work.