system
A chat on 4chan
human
Men will likely have been wondering about this throughout time.
I think important things to consider are: 
- The environment we live in
- Our material means (money and physicality), as well as non-material means like intellect/personality 
- Age

The environment we live in exposes us to sexual ideas in a very unhealthy way. What I mean by unhealthy is that it's infatuated on; it's blasted everywhere; you're considered a 'failure' if it's not something you have access to; only it's material aspects are considered to be of value, nothing else. In other times and cultures, sexual symbolism is (or can be interpreted) used as showing Unity between Opposites (non-dualism), like the Shiva/Shakti symbolism seen in the Lingam surrounded by the Yoni. Things have deeper meaning than just the material aspects of it, but in a materialist point of view, all that is considered are physical aspects. Energy is also 'built up' through celibacy practices. Basically, the times in which we live have an impact on our views. They will be in the context of mainstream thinking. So it's hard to do it in present times. It's likely to have sex dreams/wet dreams during celibacy, in the present day. 

Material/non-material means will have had impacts on men as long as such things have been valued. Women will be attracted to wealth, physicality, and attractive intellects/personalities. 

The younger you are, the harder it is to refrain from masturbation/sex/sexual thoughts, moreso these days, because the material nature is most active, in that aspect, when people are younger.

You might ask 'why bother?' Which seems a good question, especially if it is physically/mentally detrimental to scoid a physical desire. If Man is 'different' in some way to his surroundings, then he should understand that there's something 'beyond' his surroundings, perhaps 'within' himself and/or beyond physical perception. Access to such things cannot be given to He who only focuses on the material.
gpt
>used as showing Unity between Opposites
Darling in the Franxx (the anime, not the manga) is an excellent example of this. I would find it hard to believe they did not make it like that on purpose. The manga is just coomer bait.