Support is a level where demand has previously been strong enough to stop a decline; resistance is where supply has stopped an advance. They are not properties of the asset, they are memories of where large orders once sat.
Part of the effect is self-fulfilling and that does not make it less real. Enough participants watch the same round numbers, prior highs and prior lows that orders cluster there, which reproduces the behaviour that drew the line in the first place.
Levels flip roles once broken. Resistance that gives way often becomes support on the retest, because the traders who sold there now have a reason to buy back at the same price.