Regarding the “novelty wears off” thing, another side: I’ve been running for two decades, starting from a sedentary lifestyle, but it only became fun later on. I started running shortly after a friend, probably out of some youthful ambition or inferiority complex, so I ran alone and picked routes where as few people as possible would see me struggle. I don’t know why I didn’t drop it like so many other things, but I learned to yearn for it and it’s part of my identity now.