Let me first start off by saying that everyone has the potential to see a spirit. Maybe that will happen once just briefly or it could happen many times, but the thing to remember is that everyone can see them given the right factors.
Why only some people will see a ghost in a certain location can be explained in many ways but let me put it in simple real world terms that most people will understand. Let's pretend you and two friends are in the woods and you all have AM/FM radios with you. You are all standing side by side and each of you is trying to tune in a very weak signal from some small radio station. Your one friend has a great radio and they easily tune in the station clearly. Your other friend has an average model radio and they can get the signal briefly but it is filled with static. Your radio is the cheap model and you cannot get the station tuned in at all. Even though you are all standing next to each other and trying to tune in the same station you are getting three different results. Now picture each person as a "radio" that can "receive" the signals that a spirit is transmitting. One person may get the spirits signal string and they will see the spirit. The next person is not as tuned in and they may see something briefly but they may not be able to make out all the details. The third person cannot receive the spirit's signal at all and will not see anything. Hopefully this gives you an idea of how this tends to work. Each person is actually a receiver of the signals or energy that a spirit gives off. Sometimes the signal can be tuned in and other times in cannot.
There are varying conditions that may interfere with the spirits "radio signal" and may only let people with really good "radios" see them. We call these people sensitives or psychics. They are able to tune in more often to the spirits and see, hear, feel, etc. the signal and energy the spirit is sending. Some locations may make some people more sensitive than other locations and they will see something in just those places while they will see nothing in others. Sometimes even the people who have the "cheap radio" can get a brief signal tuned in and that is what happens when someone who has never seen anything all of a sudden has their once in a lifetime ghost sighting. Some of the things that can make our ability to receive these signals are our relation to the spirits, how comfortable we are in a location and our frame of mind at the time, etc. For example many people just see the spirits in their home and no where else. This is where the person is probably the most relax and comfortable and that will raise their ability to receive the signals. If the spirit is a relative or a friend you are already on that "frequency" so you will be more likely to be able to tune into that spirit.
Hopefully I haven't confused you all with
the radio and signal talk but it really does seem to be that we are sort
of receivers or spirit "signals" and this is the explanation is use at
all the lectures and most people seem to understand it better this way
than going into all the theories.