To put yourself in a risky position in order to help another person is to go "out on a limb" for them. Example: "You know I'm always here to help you and would go out on a limb if you asked me to." As you climb "out" farther "on a limb" of a tree, there is a greater chance that the limb might break and you would be hurt. Example: "I've already gone out on a limb; there is nothing more I can do for you." To go "out on a limb" is to put yourself in a dangerous position in order to get something done. Example: "I want this project to succeed just as much as you do, but I am not willing to go out on a limb."