And what causes there to be more volume on the buy-side than on the sell-side?
More volume on the buy side = subconscious or conscious perception by HERD of good prospects for the future, i.e. optimistic. In the primary trend up this can go on for years, then comes a time when you notice a tapering of volume and one of many topping formations appears on the chart. Topping formations developing = selling volume increasing
For example in a Head & Shoulders pattern, volume totally vanishes as the right shoulder is being built. Then when the neckline breaks, most often but not always, a torrent of selling volume explodes
its akin to bringing a massive locomotive to a halt and then reversing course.

