A great many Indian recipes end a cooking stage with the same phrase: cook until the mixture leaves the sides of the pan. It is an instruction about water content, expressed as something visible.
The behavior is a direct signal about moisture
A wet mixture spreads and clings to the pan because the water in it wets the metal surface and lets the mass flow.
As water evaporates, the mixture gets stiffer and its internal cohesion exceeds its adhesion to the pan, so it starts pulling away and holding together as one mass.
That transition happens at a fairly narrow moisture range, which makes it a far more precise indicator than any stated number of minutes.
It marks different endpoints in different dishes
In a spice and tomato base, leaving the sides means the water has gone and the fat has separated, which is when the base is ready for the next stage.
In a milk reduction it means the solids have concentrated enough to be shaped, and in a halwa it means the starch has taken up all the liquid it will take.
The same phrase therefore covers several distinct chemistries, unified only by the fact that each of them is finished when free water is gone.
Fat separation usually accompanies it
Once water leaves, the fat that was emulsified into the mixture has nothing holding it dispersed, so it pools at the edges and glistens on the surface.
Cooks read that pooling alongside the pulling-away as confirmation, and recipes often name both signs in the same sentence for that reason.
A mixture that pulls away without releasing fat is usually short of fat rather than overcooked, and adding a spoonful reveals whether that is the case.
Pan and heat change the timing but not the sign
A wide pan reaches the endpoint faster than a narrow one, and a heavy pan reaches it more evenly than a thin one that scorches at the center.
This is exactly why the instruction is phrased as an observation rather than a duration: the sign holds across equipment while any time given would not.
Recipes that give minutes as well are offering an estimate for planning, and the estimate loses to the observation whenever the two disagree.
Overshooting has consequences worth knowing
Past the endpoint, a spice base darkens and turns bitter, and a milk mixture goes grainy as the sugars crystallize and the proteins tighten.
Because the transition is quick once it begins, the last stage is watched closely and the heat is usually lowered as the mixture stiffens.
The safe practice is to stop at the first clean pull away from the pan rather than waiting for a dramatic version of the same sign.