Unless you have an uncanny knack for calling market trends, you are better off developing a consistent, disciplined approach and sticking to it. The most enduring trait of a successful money manager is discipline and consistency. Besides, most investors brag about their winners, while conveniently forgetting about their losers. Forget about the market's ups and downs and focus on meeting your goals. Selling too soon.
Many investors fail to understand the style with which their fund is managed.
When that style goes out of favor for several years, performance will suffer, but it is also likely to rebound when the style returns to favor. Many investors wind up selling a fund right before its performance improves, and moving into a fund whose relative performance is about to turn weak. One should sell, of course, if the fund is doing badly because it is not sticking to any discernible style. But, if the fund still fills the niche for which you bought it, stick with it. Owning too many funds.