What is the difference between an experienced investor and an average investor? 

An experienced investor accumulates his largest position at the beginning of a trend and reduces (sells in parts) it as the price moves up. 

The average investor accumulates a position as the price moves higher and holds the largest position close to the peak.

Imagine two triangles: a regular triangle (this is how an experienced investor holds a position) and an inverted pyramid (how an average investor accumulates a position).