Hey nadeentears, how are you doing?
The nerves to the penis either work or they don’t – there are no half measures, there is no such thing as them working some of the time and not at other times. Similarly, if the hormone balance is incorrect for achieving an erection then it is incorrect all the time – the hormones will not allow an erection sometimes and not at others. Finally, arteries and veins are also all or nothing mechanisms.
A normal erection needs three basic physiological requirements to be met. The first is that the nerves to the penis must be working properly and a message from the brain triggering an erection must reach the penis. The second is that the hormones in the blood must be in the right balance – this allows the spongy tissue of the penis to fill up with blood and thus achieve erection. The third is that the blood vessels to the penis (both arteries and veins) must be in good working order. This means that the arteries to the penis must carry enough blood to the penis for it to fill up, and little valves in the veins must close off properly – trapping blood in the penis.
Being able to achieve an erection some of the time, but not at other times generally means that there is nothing wrong with the three physiological requirements for an erection. Therefore, the fourth requirement is the psychological aspect. In a case where relationship issues are the problem there may be, for example, an absence of foreplay. Viagra heightens the response to direct sexual stimulation of the penis – if there is none the person may still not have an erection. ( Health24 )
best wishes,