My obsessions tend to change every 6 months to 2 years. In the past, I would power through an obsession until one day I would realize that I was getting bored of it, and then I would transition into something else. It was a relatively smooth process as I recall. But ever since the age of about 18 or 19, I find that transitioning from one obsession to another is becoming increasingly difficult.
It's because I tend to become highly emotionally involved with my obsessions - I give myself imaginary friends based on them, and I feel that if I were to transition away from them and become interested in something else, then I would "hurt their feelings". Another reason transitioning is becoming more difficult is because I feel like if my interests change, then I will disappoint the people who shared that interest with me as well as people who have bought me gifts based on that interest.