With the number of things that can go wrong in a photo, it's no surprise that it often takes a few minutes before people end up with a selfie that they're happy with.
Between the lighting, angles, focus and the little things we don't realize we're doing when the camera is on us, there are a lot of details to watch when we're figuring out whether our photos are usable.
However, focusing on those details also makes us more likely not to notice when somebody wandered into the background and took our shots in a totally different direction, as these people (eventually) discovered.