Undertand both fundamentals and psychology of the market

Market moves are driven by an ever-shifting combination of fundamentals and psychology; to be successful, investors need to seek to understand both rather than ignore them.

Mere identification of an extreme trend will not guarantee selling at an exact top or buying at precise bottoms. 

But selling above the long-term trend when markets are buoyant will produce returns above those from selling on average at the long-term trendline. 

Buying well, namely when fear pervades, gives another advantage.