Over simplistic, as any short phrase would be.
Slow to hire if you want someone to stay for more than a season. You don't want to waste training time, and you don't want other employees to have to work harder to prop up a weak link. Someone that will just be extra hands under direct supervision doesn't matter as much.
Quick to fire is a catch phrase because most of us want to give people plenty of time to succeed, and will hang on to a non-productive person to the detriment of their company. I'm more in the mindset of slow to fire, as many technicians have taken some time to pick up on all we want them to do, but once they have it, they're great. I also want to make sure I haven't failed them somewhere in the training process, so extra coaching time is spent with anyone that has issues. No one should be surprised if they're let go.