Photography is often about being at the right place at the right time. As a photographer, you may spend hours planning out the perfect shot. The angle of the sun, the time of day, the location of your subject all can make a huge difference. However, there are also those times where no matter how much you plan, you still miss "the shot". A spectator may get in the way or another object you weren't expecting. The clouds or fog may roll in. Sometimes, you simply have to "use what you've got".
The above photo of this F-22 in flight was the best shot of the series. In the very next shot, the F-22 was obscured by a tower on the pier. It would have been an amazing photo I'm sure, but this is the best one I got. Still, not bad.
It may not be the shot you planned, but you might just get something more.