Even if you're improvising, the fact that beforehand you know certain things will work helps you make those improvisations successful. It really helps to have a certain amount of knowledge about musical structure.
“The father of a daughter is nothing but a high-class hostage. A father turns a stony face to his sons, berates them, shakes his antlers, paws the ground, snorts, runs them off into the underbrush, but when his daughter puts her arm over his shoulder and says, 'Daddy, I need to ask you something,' he”