Every set of wargaming rules has was is called stress points- sections of the rules where the simulation begins to break down.
Rules that capture the feeling, tactics, and narrative of the game, but fall a *bit* short.
This is not from a critical perspective, but rather understanding wargaming RAW- rules as written.
One of these stress points, especially in older gaming systems, or one with legacy aspects from the genesis years of the 1980's, like Warhammer 40,000 is the idea of the you-go-I-go phase of the game.
Essentially, we each set up our toys on the table, and see who gets to go first.
That person moves, attacks, and use each unit, followed by the second player.
Often in you go I go systems, there is a chance to exploit the tactica known as an alpha-strike.
Delivering a powerful and focus attack in the fist phase of the game, to reduce and cripple opposing model count, before the game even starts for the second player.
If you go first, and there is no alternating units system, or chance for interrupts, on that first turn you, if an army is built to exploit the alpha strike, you can destroy opposing units before they even get to move, shoot, act or react.
In my opinion not really, BUT it is RAW.