You cannot get an erection without your brain sending the proper signals through the Endocrine system to tell the penis to engorge itself. What you have on your mind can heighten or hinder the process.
In adolescence, the human male frequently experiences numerous erections in a day. This is because his body is awash with hormones. With all those hormones the slightest stimuli: a visual, a smell, or even a light breeze causes the penis to become a phallus almost instantly. Frequently, masturbation is the only way to return it to its flaccid state.
As the male body matures the levels of hormones reduce. Even with high levels of stimuli sometimes an erection cannot be achieved. The cause of this is in the brain – stress, lack of focus, and exhaustion are the most common culprits in the lack of performance.
If one can achieve erection, ejaculation may require more intense focus on stimuli to become a reality… even in the hormone rich adolescent.
Getting a better idea of how our minds work can help us to enjoy the sexual experience much more.