A breakout happens when price clears a level that has held repeatedly. The logic is that the orders defending the level have been consumed, leaving nothing immediately above to slow the advance.
Volume is what separates a real breakout from a false one. A break on volume well above average reflects genuine repositioning; a break on thin volume is much more likely to reverse, trapping the traders who chased it.
False breakouts are common enough to be traded deliberately. Price pushes just beyond a well-watched level, triggers the stop orders resting there, and immediately returns into the range. Waiting for a close beyond the level, or for a successful retest, filters many of these out at the cost of a worse entry price.