Question higher dex attacks opponent first each round

Higher dex combatants attack first each round, e.g.:

The dextrous cat hits the slow turtle.
The slow turtle misses the dextrous cat.

instead of:

The slow turtle misses the dextrous cat.
The dextrous cat hits the slow turtle.

A more refined system can allow some faster defenders to hit an attacker first of all and first each round, and some to negate the attacker's initial attack by noticing it, instead of granting anyone faster two attempts in a row. Many game variables can be interpreted to affect which character attacks first even when a specific player clearly has. Alertness and speed seem like the main factors in what is represented by these sentences:
A player commands a character to attack a mobile.
The mobile hits the player's character.
(or)
An algorithm commands a mobile to attack a player's character.
The player's character hits the mobile.