It isn't always a case of blood flow,Chaz. In ED, the mind is willing, the blood can flow in, but nothing stops it from flowing out of the penis...so it gets hard but quickly soft. The blood control valves don't seal the way they used to. What is does mentally to a man can ruin his appreciation for sex, cause he fears it will happen again. In other words, too many failures perpetuate the problem further. Meanwhile his wife/ girlfriend lives with this horrible frustration....not a very happy situation. He cannot even spank the monkey if he so desires.