The instruction to cook only with wine you would drink is sound advice pointed in the wrong direction. Heat transforms wine so thoroughly that its drinking qualities predict very little about its behaviour in a dish.
The volatile parts leave first
Alcohol and the lighter aromatic compounds evaporate quickly under heat, and these carry most of what makes a wine pleasant to smell. The nose of the wine is gone within minutes.
What remains in the pan is the non-volatile fraction: acid, sugar, tannin, pigment and extract. That residue is what actually seasons the dish, and it is the part nobody assesses when choosing the bottle.
A wine chosen for its perfume therefore contributes almost nothing distinctive once reduced, and the money spent on it evaporates along with the aromatics.
Reduction concentrates what stays behind
Removing liquid concentrates everything that does not evaporate, so a wine's acidity and any residual sugar intensify substantially.
A wine that tasted balanced in the glass can produce a sauce that is aggressively sharp or unexpectedly sweet after reducing by half.
This is why off-dry wines behave unpredictably in savoury cooking, since sugar that was barely perceptible becomes a defining element.
Tannin becomes a texture problem
Tannin does not evaporate and concentrates along with everything else, producing bitterness and a drying quality in the finished sauce.
Heavily oaked wines contribute the same way, and oak-derived compounds concentrate into something closer to bitterness than to vanilla.
Lightly structured reds therefore reduce more gracefully than powerful ones, which inverts the usual hierarchy of quality.
Oxidised wine is not automatically ruined
A bottle that has been open too long has lost the aromatics that heat would have removed anyway, so the loss is largely irrelevant.
What matters is whether the wine has turned volatile and vinegary, since that acidity survives cooking and carries into the dish.
The genuine test is whether the wine still tastes clean rather than whether it still tastes good.
What to actually select
Dry, moderately acidic wines with restrained oak and modest tannin behave most predictably across a wide range of dishes.
Matching the wine in the pan to the wine at the table is a reasonable convention, though the link is one of style rather than necessity.
The one firm rule is to avoid anything sold specifically for cooking with salt added, since the seasoning becomes uncontrollable once the liquid reduces.