An erection can also be achieved through erotic fantasies, memories, sounds, touches and sights. Physiologically-speaking, the penis elongates because of the sudden flow of blood to the genital area.
In some cases, the penis may not be able to achieve or maintain erection. This condition is known as erectile dysfunction and can happen for a number of reasons. In said cases, couples may choose to use penis extenders or strap-on dildos to facilitate intercourse. In other cases, medication or sex therapy might help the penis reach an erect state again.
Erection is not required for orgasm. People with ED may choose to use flaccid-friendly sex toys to achieve pleasure and orgasm without the need for an erection.