A couple years ago, one friend of mine had surgery on her wrist and another friend was in a rollover ATV accident and shattered his wrist. Both of these folks carry regularly.
The ATV guy had practiced regularly with one handed shooting. He also regularly practiced "as if" he was a lefty, using two hands. So once the initial fog from the injury and drugs cleared up, we went up to the range. He quickly ran through the basic manipulations, smiled, and was good to go on carrying as always.
The wrist surgery gal wasn't prepared. She'd never done one-handed manipulations before, although she had at least shot one-handed a few times. She'd also never practiced "as if" she was a lefty. She spent several very long and tiring sessions on the range trying to get up to speed with one-handed work. It was frustrating and very difficult for her. Eventually she was good to go, but it was a really steep learning curve. Later, as she healed up, there came a day when her injured wrist was healed enough that she could have been shooting two-handed as a lefty -- but she'd never really practiced as a lefty, and knew none of the basic manipulations from mirror image. So she had even more work to do and more to learn.
It's just a LOT easier to learn these things in advance of needing them, when you are not rushed for time or hazy from pain.
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