What it means
Trapped traders and late buyers act at the old level, which is why retests often hold.
In practice
The flip is one of the most dependable behaviours on a chart. After resistance breaks, those who sold there are losing and want to get out at their entry price, and those who missed the break want in. Both mean buying at the old level.
Traders mark broken levels and wait for the first return, entering with the stop on the far side.
What to watch for
The first retest is the most reliable; every further one weakens the level. If price returns and slices straight through, the flip has failed and the earlier break was probably false.