I planned to propose to my girlfriend at sunset on the coast. We walked along a path and I got out my camera, ostensibly so we could take photos of ourselves using a small tripod I brought. I was going to take a few photos using the camera remote, then propose and keep taking shots to capture the moment.

As I was setting up the tripod on a bench, and man who was walking by offered to take a photo for us. I didn't want to explain what was going to happen, so I declined. But he insisted that he had the exact same camera, and would be happy to take some photos.

I lowered my voice so my girlfriend wouldn't hear, and said "Ok don't react at all, but I am about to propose to my girlfriend." He nodded in understanding and calmly took the camera. He took a few posed shots and then gave me the signal. I got down on a knee and proposed (completely forgetting what the speech I had prepared, of course), with him taking photos all the while. I'm certain that the photos he took (in manual mode!) turned out much better than what I would have captured at sunset/dusk, via remote.

A year or two later I mentioned to my then-wife that it would have been nice had we invited the man to our wedding. She laughed and said that she always assumed he was a photographer whom I had paid to be at the location at that time. It took quite some convincing before she understood that he was just a Nikon photog who was in the right place at the right time.