Does every experience you ever have affect you long term? I expect your first day at school has a role to play in who you are at the age of 40, but what effect does waking up for your thousandth school-day have? (Assuming that you wake up in a fairly typical fashion on that day.)
Are there experiences that affect you only in the short term, baring nothing whatsoever on your character at a later time? Watching a film might be an example of this, as might spilling your drink or dropping your toothbrush. These events affect you for a while, but do they have any lasting affect, however small?
Are you affected by experiences of which you have no recollection from the night before while exceedingly intoxicated?
By experience, I mean anything at all you were conscious of - even in a small way. By "conscious of" I do not mean that you thought about it, only that it was for even a moment part of the unity of your conscious mind. This then opens up the possibility that you are then affected by things that you are not conscious of. To these 'things', the same questions apply: does every unconscious experience affect you long term? Are there unconscious experiences that affect you only in the short term? These two questions being very hard to consider I feel it's best we ignore them at least until we've considered at least the conscious cases.
I have no answer to these questions, I ask them because they are interesting and because it would be nice if others pondered them too. One might wonder whether we are only affected long term by only things we remember or perhaps only by critical experiences. What might these 'critical experiences' be? Experiences that are emotional, significant in one's life, or things that affected you over a long period of time could all be candidates.
In my earlier post "Why Don't I Remember Everything?", I said: "generally, we remember what is often used or linked with emotional stimulation (or, I suppose, strongly linked with something else)". According to this, a critical experience is an experience one remembers. However, I strongly expect that the critical experiences for long term memory are different from the critical experiences that affect you long term. I expect that the chance of an experience affecting you is greater than the chance of it becoming a memory. This chance may even be 100%. This is because if you experienced it, your brain processed it. I think that your being affected by an experience depends on whether the act of your brain's processing of it changes how it processes the next data to come through. The question of whether some experiences affect you only for a limited time depends on whether the brain's process is affected only for a limited time. So, discover the process (assuming there is one (that will help us answer this question) and that it can be discovered) and we discover the answers to this question! Although, it can be discussed philosophically with interest without ever thinking about the brain like this.