They are both tougher and weaker than you think; like every other animal, really.
As others have said, if you start with healthy stock, then you've already saved yourself 50% of potential trouble. If you have a good, solid, predator proof coop (and a run for an added bonus), then you're over halfway there! Good nutrition, plenty of water, and space for them to do their chicken things and you'll be amazed at how simple it is a vast majority of the time. However, like all things, chickens can get hurt or sick, but they are typically not especially prone to it if you've got everything else that I mentioned covered.
For an example, I was stunned at how easy several of my girls kept getting bumblefoot. I got more proficient at performing the minor foot surgery that requires than anyone should have to, but when I repeatedly got pieces of thorn out of the wounds, we knew what to do. Took me and my DH 6 months to locate and eradicate every piece of thorny bramble we had on our property, but we haven't had an issue since. So in instances like that, you live and learn and adapt! But once I'd bandage those feet up, they'd go running off like they didn't have the gaping wounds on the bottoms of their feet that they did. When my roo got a broken toe in a tangle with two dogs roaming at large, he was still running around the yard like nothing was wrong.
So ridiculously tough buggers, too.

As others have said, if you start with healthy stock, then you've already saved yourself 50% of potential trouble. If you have a good, solid, predator proof coop (and a run for an added bonus), then you're over halfway there! Good nutrition, plenty of water, and space for them to do their chicken things and you'll be amazed at how simple it is a vast majority of the time. However, like all things, chickens can get hurt or sick, but they are typically not especially prone to it if you've got everything else that I mentioned covered.
For an example, I was stunned at how easy several of my girls kept getting bumblefoot. I got more proficient at performing the minor foot surgery that requires than anyone should have to, but when I repeatedly got pieces of thorn out of the wounds, we knew what to do. Took me and my DH 6 months to locate and eradicate every piece of thorny bramble we had on our property, but we haven't had an issue since. So in instances like that, you live and learn and adapt! But once I'd bandage those feet up, they'd go running off like they didn't have the gaping wounds on the bottoms of their feet that they did. When my roo got a broken toe in a tangle with two dogs roaming at large, he was still running around the yard like nothing was wrong.
