Stress
The biggest stress in your life will be your customers. By, like, a lot. Typically, when you're called out to unlock a house or a car, the person you're attempting to help had somewhere to be about twenty minutes ago. More often than not, you won't arrive to cheers and happy faces; you'll arrive to scowls and the unspoken "what took you so long?"
Many of these people will understand that standing off to the side and letting you work is the best way to help; a few will think you'll work faster if they stand over you shouting commands and complaining about your rate of work.
Another big issue will be the travel. The professional locksmith does not have the luxury of staying put and making money. If you want to serve your customers, you have to get to them. That means traffic, car accidents, freeways, and all the other parts of driving that seem a lot more fun in Grand Theft Auto. Add to that the monster of a vehicle you will be driving―usually a cargo or conversion van filled with heavy and expensive tools―and you can imagine how fun driving back roads in winter can be.