If you fall, "pick yourself up" is one way of saying "to stand up again." "To dust" can mean "to clean dust off." "To dust yourself off" can mean "to clean dust off yourself." Your clothes will probably have some dry powdery dirt or dust on them. If it is not too much, you can use your hands like a brush and "dust yourself off" or "brush yourself off." It is an idiomatic phrase, possibly popularized by a 1936 song: https://youtu.be/AGUsRGuZb6k?t=36 "Now nothing's impossible, I have found, for when my chin is on the ground-- I pick myself up, dust myself off, and start all over again. Don't lose your confidence if you slip, be grateful for a pleasant trip-- And pick yourself up, dust off, start over again!" Some other common expressions, sayings, and catchphrases with similar meanings: "Get back on the horse!" (If you are thrown from a horse, it's often said you should get back on it and start riding again immediately before the fear has time to sink in). "Shake it off." "Let it roll off you like water off a duck's back." "If at first you don't succeed, try, try again."

It’s equating the bad date to something like getting thrown off a horse. There you are lying on the ground, covered in dust. Do you just lie there, or do you get up, brush the dust off, and get back on the horse…?