This is based on a strategy called value area. The upper trendline represent the upper limit of the value area, lower trendline represents the lower limit and the middle trendline is the control price.
Notice how price is respecting these levels marked as circles, and how price is gravitating around control price, the classic example being when price breaks the upper limit of value area.
The principle behind this value area strategy is price is pulled into it, marked by 1st arrow to the downside, price aggressively comes to the lower limit of value area and then reverses its direction, the same movement can be anticipated in coming sessions marked by 2nd arrow to the downside.
Notice how price is respecting these levels marked as circles, and how price is gravitating around control price, the classic example being when price breaks the upper limit of value area.
The principle behind this value area strategy is price is pulled into it, marked by 1st arrow to the downside, price aggressively comes to the lower limit of value area and then reverses its direction, the same movement can be anticipated in coming sessions marked by 2nd arrow to the downside.