We all have habits, even if we're only dimly aware of them.
For instance, when you throw your purse or bag over your shoulder, it's probably always the same shoulder. And when you lift something up off the ground, you'll probably use your dominant hand. These may seem like small things, but repeating these same motions on the same side for decades can lead to back, neck, and shoulder imbalances.
Thankfully, this isn't hard to fix. Just change the way you move every now and then. So if you usually carry your purse on your left shoulder, carry it on your right shoulder for a couple of days. Or, if you have a big bag with two straps, put it around both shoulders.
The key, as always, is variety and balance.