You are the average of everything you have done thus far in your life. All of your actions, meals, learning, friends, everything; blended into one.
It surprises me when people think that one single thing, good or bad, is going to change them forever. One cookie is not going to make you unhealthy, just like one salad is not going to make you healthy. You are an average of the food you consume. One workout is not going to get you in better shape, just like missing one is not going to knock you out of shape.