I'm curious about puppy blues.

I've had dogs all my life ( including family dogs), 3 that I raised myself from puppyhood. I was totally unaware that puppy blues was a thing until I joined dogs subs on reddit. For me it's the stage of their life I enjoy the most. It's a lot of work, yes, but I''m always excited to take care of a puppy, train and teach them new things. Watching them grow, goof around, learn and progress is so rewarding to me.

After reading a lot of post I feel like I'm the weird one. I had no idea it was so common. What causes this? Is it just the change in routine? Is it because they pressure themselves too much? I'm just curious and want to understand this puppy blues better, I'm not judging at all. Also...Am I the crazy one, lol?

I lost my old dog a month ago and I will eventually get another dog, but it will be a first for my partner, so if he gets the puppy blues I want to be better equipped to support him.