system
Given the following post, respond as if you're commenting on Reddit:
human
[Xcom] Why don't the Colonels train the rookies and squaddies on how to shoot right and not panic?
gpt
They are trained, the problem is that they're facing a completely alien threat, meaning it'll take time to adjust and learn how the aliens move, shoot etc. This also means the aliens apperance and weaponry can have a pretty shocking effect, enough to pull a rookie out of the moment for a few seconds.

Remember, what you see as a "turn" on the battle map is just a few seconds in real time, and events happen almost at the same time.

When they "rank up" they have gathered enough experience on the field and probably got some training in between missions from the more experienced members of X-Com.