A penalty is a straightforward physics problem dressed up as a psychological one. The distance, the reaction time available to the goalkeeper and the size of the goal determine which strategies work.
The goalkeeper cannot wait and still reach the corner
A struck penalty reaches the goal in a fraction of a second, which is less time than a goalkeeper needs to perceive the ball's direction, decide, and move his body across the goal.
That arithmetic means a keeper who waits to see the shot can only save balls hit near him. To reach a corner, he must commit before or as the ball is struck.
Every element of penalty strategy follows from this: the keeper is guessing, and the taker is trying to make the guess irrelevant.
The corners are effectively unsaveable when found
A ball placed inside the post at a comfortable height is beyond a diving keeper's reach even with a correct guess, provided it is struck with reasonable pace.
This is why elite takers aim for a target that is generous in width but demands accuracy of half a metre or so. The reward for hitting it is close to certainty.
Raising the ball increases the safety margin but also increases the chance of missing the target altogether, so most takers choose a height around the keeper's hip or lower.
Power costs accuracy without buying much
Beyond a certain speed, additional pace does not meaningfully reduce the keeper's chance of reaching the ball, because he is already committed before contact.
What extra power does reliably reduce is the taker's own precision, since a full swing is harder to control than a firm, balanced strike.
The exception is the shot aimed centrally, where power is the whole point, since a keeper who stays put will save anything struck softly down the middle.
The stutter run-up shifts who commits first
Slowing or pausing during the approach is an attempt to make the goalkeeper move first, converting a guess into a visible cue the taker can exploit.
Rules limit how far this can be taken, and feinting after completing the run-up is penalised, so the technique operates in a narrow window.
It also carries a cost. A disrupted approach makes a clean strike harder, which is why takers who use it tend to aim at safer, more central targets.
Goalkeepers work on information rather than reflexes
Since reaction alone is insufficient, keepers rely on preparation: tendencies of individual takers, body orientation during the run-up, and the position of the standing foot.
Those cues appear late and are unreliable against a taker who has decided in advance and does not adjust, which is the main argument for choosing a corner and ignoring the keeper entirely.
The remaining edge for the keeper is delay and presence, staying upright long enough that a taker who was watching him is tempted to change his mind at the last moment.