When do you shelve a manuscript?

I hear of many writers who last year were querying one book but this year they're querying a whole new book. They shelved the previous book after a few requests led to rejections.

I've been querying Daze for... oh, um, well... awhile. But I will admit here and now that I made a common writerly mistake and queried TOO SOON. Lately, I've had some requests. Some have led to R's, others I'm still waiting on. My plan is to give Daze another edit once I hear from these others and then send out another round of queries.

But should I? Or is it time to shelve it?

I know first books are rarely the ones that get published. But in my own defense, I've spent over two years making this book the best I can make it. I feel like this book is the "one." But maybe I'm just too attached? Maybe I need to just let go and I can't.

I feel like after one more round of queries, I probably will shelve it and focus on Sway. That's my plan for now, anyway. But I am wondering, when do you shelve? And what makes you shelve?