In practice
A retest lets traders who missed a breakout enter with a small stop: the entry is at the broken level and the stop goes just beyond it. A level that holds from the other side also confirms the break was genuine.
The cleanest retests return on smaller candles and lower volume than the breakout, then turn with a clear rejection.
What to watch for
Strong breakouts often never come back, so insisting on a retest means missing some of the best moves. A retest that pushes deep back through the level is a warning that the break is failing.