Most of the photographers out there agree with the stance that a photo that isn't shared, does not exist (in other words, if you are not willing to share/show a photo, you better not make it at all). Well, I belong to the minority and think that this stance isn't necessarily true. Indeed, we capture moments, yet we don't do this for the likes of others or for public appreciation but for our own sake. Primarily, a photograph is a form of visual contemplation, a creation closely connected to our inner being. What we do with it depends on many things but it isn't mandatory to share it with others. Not doing so doesn't make a photo less valuable to us. Even though a photo can be a means of alternative communication, such a creation isn't always meant to serve this purpose. This also happens with other forms of art such as painting, sculpture, music etc. I always adopt the notion that we take photos for us, not for the others and under these conditions, we may keep some of our creations for our eyes only. Nothing wrong with that.
It is true that most of the time, a photo can be more than an expression tool. It can be a communication and messaging tool as well. Some types of photos really need to be shared or else they shouldn't be taken at all. Most of them are related to social matters (war, child abuse, poverty, depression etc.). However, there are some other types of photos that usually don't serve such a purpose (fine art, landscapes, etc) and there are occasions that the photographer really needs to keep such a photo to himself as he might consider a specific photo to be unique, intimate, something special that he doesn't have to (or need to) share with others. It might be a small selection of photos or a certain portfolio that was created for his eyes only, and this happens for reasons he doesn't need to explain to others. Personally, I have come to such a situation for just a couple of photos that I made and I'm confident that this stance has been followed by many other photographers as well.
So, when we take (make) a photo, what we primarily do is that we create something, a visual creation and most of the time we make a photo as a means to express something. After that we either share this photo or we don't. Either choice is irrelevant to the value of a photo. If our purpose is to keep a specific photo in private, that doesn't mean that what we've created doesn't hold a value.
An artist has reasons to create that ought to be irrelevant to what other people expect from him. Being selective to what you share is also a type of expression. If our need is to create a whole alternative world through a photo and ponder on it, "live" in it for some seconds, minutes or more, solely by ourselves, this is also a form of expression and a valid reason to take a shot.