Why the gap matters at all
Tennis allows roughly twenty-five seconds between points, a stretch that other sports rarely offer between individual actions and one that is long enough for the emotion of the previous point, frustration at an error, elation at a winner, to bleed into the next one if left unmanaged. Unlike a rally itself, this gap contains no external demand forcing a player's attention forward, which means it is entirely on the player to use it well or waste it.
The routines players build to fill it
Most players fill this window with a consistent, almost ritualised sequence, turning away from the court, adjusting strings, bouncing the ball a fixed number of times before serving, that has little functional purpose beyond interrupting whatever emotional state the previous point left behind. The specific ritual matters less than its consistency, since a repeated routine gives the mind a familiar anchor to return to regardless of whether the previous point was won or lost.
Why it matters more under pressure
This reset becomes more visibly important as a match tightens, because tension amplifies the cost of carrying frustration or anxiety into the next point, and a missed reset at a crucial score can compound quickly into two or three lost points in a row. Commentators who describe a player as having good on-court composure are usually describing exactly this skill: not an absence of emotion after a bad point, but a reliable, practised way of setting it aside before the next one begins.