There are few absolute statements you can make about a penis. One might be that penises are unpredictable and unreliable. You may have 100 experiences where your penis (or the penis you're with) responds as you expect and responds in concert with the way the rest of the body feels. But that doesn't mean that the 101st time an erection will not give way to a soft penis before its time.
If you have a penis, or if you have regular access to one, you've probably experienced this; a time when an erection was desired but didn't appear. Or when an erection came, but then went soft. This is what it means to have a penis. It's common. While sometimes it can be a sign of a problem, other times it's just part of life; things go up, things come down.
Why Erections Go Soft
To understand the many reasons why an erection might have gone soft you should start by understanding how erections work. Knowing the multiple systems involved in making an erection happen can leave one with an appreciation that they ever happen at all. The bottom line is that everyone who has a penis will have the experience of having an erection, feeling like they really want to have sex and then losing that erection at some point that isn't particularly convenient for the sex they want to be having. Let's consider some of the most common causes of losing an erection:
Distraction: After the first couple times you have sex it's pretty easy to get into a kind of autopilot when engaging in sexual activity. It's not that we aren't enjoying ourselves, but we have a sense of what's next, what's expected of us, what we might be getting in return, etc. And it's easy for us to go along with what's happening even if we're a little distracted. Maybe we're thinking about work, or about something from our sexual past. Maybe we're thinking of an argument we had or are worried about having, or about who is going to let the dog out before bed.
What Does It Mean? Being distracted means being disconnected, your mind going one place while your body is somewhere else. I don't like personifying body parts, but the penis is a pretty sensitive measure of that kind of distraction. Some people can keep an erection even if they aren't feeling it, but for others, even a minor distraction can result in a soft penis. We all experience distraction when we're having sex. And if it happens now and then it may be nothing to address. But if you are consistently finding yourself distracted and it's playing out through losing an erection, there maybe something in yourself or in your relationship that needs to be worked through.
Desire: There's a common belief that anyone who has a penis is ready for sex anytime, anywhere, anyhow. It's common, but false. No one wants sex all the time. And sometimes, we want sex more than others. We can start having sex with someone we're into, maybe we love them. It's not that we aren't enjoying it, but the truth is that we'd rather be sleeping or maybe we just aren't feeling great about our body at the moment. If the desire to have sex in the moment isn't there, again, the penis may respond.
What Does It Mean? Just because you don't feel like having sex in the moment doesn't mean you don't want your partner in general. Often it's the partner of the person who loses an erection who worries that it must "mean" something. If they can't get an erection doesn't it mean they don't love me? Don't desire me? If this happens now and then, clearly that's not what it means. But it's for you to think about and be honest with yourself about how much you desire sex with your current partner. If the answer is, "not much," then you need to figure out whether it's because of the kind of sex you're having (maybe you want something else) or is it because of who you are having sex with? Or is it for another reason that has to do with how you feel about yourself?
Physical Origins: Erections happen as a result of many physical processes. Body parts have to move, expand and contract. Nerves have to respond to stimuli, and blood has to flow in the right directions at the right pressure. If any part of your body is working differently, the result may be no erections at all; sometimes it might be that you get an erection but then lose it before you're finished with it.
What Does It Mean? Sometimes an erection will go away because of something that's happening in your body, and this is the reason it's so important to talk with a doctor and have a physical examination if you find your erections are going soft with any regularity. Losing erections can be your body's way of pointing out that something else is going on, something that requires your attention. You don't need to jump to the conclusion that something terrible is wrong with you, but it's recommended that you get checked to rule that out.
Psychological: Being distracted may be a momentary thing, but your psychology absolutely plays a role in erections. This includes things like all your previous sexual experiences, especially any negative or coercive sexual experiences you've had. It also includes your sense of yourself, your sexual and gender identity, and how you're feeling about it in the moment. Finally, interpersonal or relationship issues that you may have and may not be talking about can play out in your sex life in the form of losing erections, often at particularly significant moments.
What Does It Mean? What it means depends on a lot. It doesn't (necessarily) mean you need to end your relationship. It doesn't (have to) mean you're having sex with someone you aren't attracted to. Or that you really want to have sex with someone of a different gender or orientation. It isn't (always) a giant sign pointing to buried childhood sexual abuse. Some people can fake it and some people's bodies go along for a while. But if your erections aren't lasting and you've ruled out the physical stuff, then talking with a counselor or sex therapist may be recommended.
Medication: There are many different kinds of medications that cause erectile dysfunction. Some make it difficult to get an erection and others increase the chances that you won't be able to maintain an erection for the length of time you'd like to. If you're taking any medication, talk to the doctor who prescribed it and ask about sexual side effects. There may be alternative medications you can try that won't impact your erections the same way.
It's important to remember that it is not realistic to think that you'll get an erection whenever you want or that it will stick around as long as you'd like. So much sexual performance anxiety arises from unrealistic expectations we have of our bodies. And that anxiety can make it worse and can actually be another cause of losing your erection. There may be nothing wrong with you other than you are worried about losing an erection.
Dealing with this almost always means talking. Talking with a partner, talking with your doctor, talking honestly with yourself.