Where it sits in a shot
A flick happens in two parts. First comes a fast movement, mostly planned before your hand starts, that carries the crosshair close to the target. Then comes a short correction that lands it. That correction is the micro-adjustment.
The main movement can stop short of the target or carry past it, and the micro-adjustment fixes either. A flick that needs one small correction is normal. A flick that needs several usually means the first movement was off by a lot.
Why fewer means faster
Every correction costs time: the hand slows, your eyes check where the crosshair ended up, and the hand moves again. A first movement that lands inside the target skips that loop completely, which is why improving the main movement usually buys more speed than making corrections quicker.
Training both sides
Flick trains the first movement, so that it needs less correcting. Tracking is continuous micro-adjustment: you are correcting constantly to stay on a moving target. Your sensitivity matters here too. At a lower sensitivity the same small correction takes more hand movement, which makes it easier to control and slower to make.
Overcorrecting
The common way to waste a micro-adjustment is to make it too big. A correction thrown as fast as the flick itself carries past the target the other way and needs a correction of its own, so one miss turns into a back-and-forth.
Near the target, a correction should be small and slightly slower than feels natural. If you notice yourself swinging past heads and back, that is overcorrecting, and the common aim mistakes guide covers it alongside the other habits that cost time.