After 30 years of shooting weddings, I still find myself checking once, twice and a third time on almost everything I do. The level of "pre" wedding work I do is enormous so that I DON'T find myself flailing on the day of. I always have a back up plan for inclement weather and a back up plan for that plan.
Even with everything I do (and the above doesn't really cover the extent) I'll sometimes find that I'll go to the park for the outside shots, never having changed my iso from the church. It happens. And if it's a stressful day, it always seems to get worse.
It's a mentally tiring day for me with all the attention depth of field, light directions, iso and composure demand. Getting to the reception is a relief because the tough part of the day is over and I can relax and have fun.
But I love it and can see myself shooting until I can no longer pick up a camera.