Stress
Whether you call it reverse karma or just part of the gig, helping relieve others' stress can be, well, stressful. A big move involves lots of details and compromises, and things like canceled flights—which you can't control—can take your perfectly choreographed plan and turn it into a nightmare. Stressful? You betcha. Now consider this happening to multiple clients at the same time.
Yeah, it's a little stressful.
That's why someone very sharp invented the "back-up plan." You should make good use of those. As a pro, you anticipate what could go wrong and plan a work-around. A little pro-activity on your part can save you a lot of headaches and provide the added bonus of making your clients realize you're a genius.