That's what makes a photographer happy.
Yes, it is good to have a good camera, with a charged battery and large capacity for high quality photographs. But planned photographs can give you only so much satisfaction.
Serendipity gives you the extra.
While traveling East along the shore of the Rouge River of Southwestern Oregon, I looked up at the right time from the right place and caught a glimpse of an eagle's nest. So I stopped and moved until there was just the right angle for a clean photo of it.
The serendipity wasn't finding the eagle's nest but that a parent bald eagle was returning to the nest and thus arousing its lone inhabitant from his slumber.
So hearing his parent's cries as it approached the nest, the young eagle climbed up to its edge as daddy or momma, which ever the case was, landed.
Then the young eagle imitated his parents wing actions several times.
Yes, I took dozens of photos, and stayed as long as I could. I was just out of range of my camera's ability to get good details an my ability to hold it steady, but I was extraordinarily please to have had the experience anyway.