Young men often feel unsure of themselves sexually and every other way. The pressure of sexual thoughts and the relentless basic drive to procreate allied to intense visual stimuli, the smell, shape, body heat and physical feel of the female body can combine to overwhelm the senses and the young man comes too soon. Premature ejaculation can happen outside the body or an instant after penetration. Whenever it happens, it is a disappointment for them both, and one failure can lead to another, and then start a downward spiral of worry, anticipation, fear and more failure.
However, young men are very resilient, and don't actually need much to get them sorted out. This metaphor can encourage the mind to hold back until the right moment.
This script is available in the Erotic Scripts Collection