I can't imagine having to perform as a wedding DJ or photographer. The pressure must be intense, as there are no second chances.
My wife and I had a flower shop several years back, and that was hard enough. But we could take our time making sure everything looked great and then get out of there before the festivities started.
Other than that, I've only been to three weddings in my life, not counting my own (which was a quiet justice-of-the-peace ceremony on the beach).
You're so right! It is very high pressure and also very underappreciated. As a general rule of thumb for photographers, one should have had some practice at a few weddings with the help of some mentoring before taking on their first one solo.