Sometimes in life there are messengers who deliver a life-altering message to us, whether it is expected or not at the time. Other times, we have experiences which end up changing how we think from this day forward, and similarly these are sometimes expected and sometimes not. Such messengers and experiences can mean a lot to us, but this does not mean we need to hold onto them forever.
One great example is school. We (hopefully) learned a lot in school, and enjoyed our time there, but when school ended, we didn’t try to stay. We left, knowing that our experiences and our teachers prepared us for being out of school. When school ended we packed up and left, probably sad about leaving, but appreciative and ready to move forward. Similarly, there might have been a teacher who really meant something to us, inspiring us to take a certain path or think differently. And similarly, we do not take that teacher with us in our next adventure.
When it is time to let go, it is time to let go. Thank the people, places, and things which helped shape you, and move forward. You do not have to hold onto anything other than memories. Being grateful does not mean you need to hold on forever.