Penile total erection but not hard, what is the reason

Patient's question:

Patient gender: Female
Patient age: 21
My husband's penis gets erect immediately when I touch it, but it always fails to stay hard during intercourse. Why is it that it gets erect so quickly, yet it seems to lack endurance?

Doctor's answer:

Hello, the issue of weak erection is a manifestation of depleted kidney essence. This is related to the damage caused by frequent masturbation to the body, and it is not related to prostate problems.