The inability for a man to achieve and maintain an erection for sexual intercourse is known as Erectile Dysfunction (ED). Millions of men are affected by Erectile Dysfunction, and many men experience it at some point in their lives, although not psychologically affected by it.
Erectile Dysfunction (ED) can be total or partial. Where total ED is concerned, a man will be unable to achieve an erection during any sexual activity. This normally happens from damage to the sexual organs. In the case of partial ED, a man will be able to achieve erections infrequently or only partial erections for a short time. 
Men feel a great pressure to perform when engaging in sexual intercourse. Men that suffer from ED will feel like they are failures. This sets off a vicious cycle where psychological stress makes him unable to achieve an adequate erection. The inability to have an erection then causes him anxiety, which further hinders him from an erection.
Many men will at some point experience a passing episode of ED. This is temporary and they should not worry. It can be caused by excessive stress from work, money, depression or relationship troubles, which in turn leads to psychological impotence. 
There are physical factors that can lead to a man developing ED. These factors can form over time, depending on your body’s health. Some of these physical conditions include;
Low Hormone levels.
Nerve or spinal damage.
Side effects from Prescription drugs or narcotics.
Treatment for ED can normally be successful and allow a man to enjoy a fulfilling sexual life. There are a number of treatments such as;
Penile prosthetic implants
External vacuum devices
Sleep and relaxation
If you are suffering from ED, you should consult a doctor, who will then provide you with the treatment necessary. Learn about Impotence here