Returns if this is the first time this hook was predicted.
This is useful for one-time logic in your SWEPs PrimaryAttack, SecondaryAttack and Reload and other (to prevent those hooks from being called rapidly in succession). It's also useful in a Move hook for when the client predicts movement.
Visit Prediction for more information about this behavior.
An override for GM:KeyPress in the gamemode Trouble in Terrorist Town, to work around the hook being called multiple times.