What do you call a situation when you can't find the things you are currently looking for but finding it when you're not looking for it?

What will be the best word or term to use in that kind of situation?
For example, I am currently looking for my Nursing book inside my house but after days of searching, still no success and I already gave up. However, few weeks or months later I accidentally saw it under my bed when I am cleaning up my room.

I am thinking of the word "Coincidence" but I am looking for a more precise word. Luck? hmmm. Not quite sure.

If you're saying it took you too long to find the book, try

Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

If you just want to point out that the universe works in weird ways, you can say

Finagle's Law: The perversity of the universe always tends toward a maximum.

When it's vexing, frustrating, I blame mean old "Murphy's Law." When it's unexpected good fortune, it's sweet sister "Serendipity."