Polar Patterns and Placement
A microphone's polar pattern describes how its sensitivity changes with direction, and the real skill is learning to aim a mic by its dead zones as much as by its front. Each pattern has a different shape of "deafness" that you can point at your problems.
An omnidirectional mic hears equally in every direction. It has the most natural, open tone but offers no rejection at all. A cardioid hears the front and is deaf directly behind it, at 180 degrees — the everyday pattern for live work. A supercardioid tightens the front pickup but trades a small lobe of sensitivity at the rear, with its deepest rejection sitting near 126 degrees off-axis. A hypercardioid is tighter still, rejecting most strongly around 110 degrees with an even larger rear lobe. Knowing where each pattern is deaf is what lets you place a vocal mic so the monitor wedge sits in its quietest angle rather than straight behind it, where a supercardioid would actually pick the wedge up.
Directional mics also do something omnis cannot: they show proximity effect. As the source moves in close, the low frequencies rise, because these mics respond to the difference in pressure across the capsule. A singer working right up on the grille gets a warm, chesty boost below a few hundred hertz; back them off and the tone thins out again. You can use that as a tool or fight it as a problem, but either way it is part of the instrument. All of which leads to the same practical truth: moving a microphone a few centimetres changes its tone, its isolation, and its gain-before-feedback more than any amount of EQ further down the chain.
Position solves problems that EQ cannot.