don't get (out) over your skis

Don't think or act impetuously or preemptively without knowing the reality of a situation. I always tell entrepreneurs, "Don't get over your skis." The last thing you want to do when you're starting a new business is to take on more risk and responsibility than you can actually handle. Come on now, don't get out over your skis—you have no way of knowing what Shelly's thinking. A: "I'm kind of freaking out about the whole thing." B: "Now, don't get out over your skis. Until the doctor calls, you're just guessing at scenarios anyway."