I recently coordinated an event that required the people involved to pull their own weight. If one person faltered, the event would collapse like a house of cards. As the person coordinating the event, it is your responsibility to recognize things that could go wrong. YOU must analyze each situation, and, no matter how much someone might say it is covered, go with your gut feeling when you believe that something may go wrong.
Here is an example from this event. Electrical power was being provided to certain elements of the event. In the event that the power failed, there was a generator available to support these certain elements. There was, however, an additional element that was supposedly coming with their own generator. When I heard this, I became skeptical. Since the company bringing this element was also bringing another element that we were providing power for, I felt it highly unlikely that they thought they would have to provide power for this additional element. I never directly spoke to the company and was assured by the intermediary I was dealing with that they would bring a generator. Having done thousands of events, I decided to have the local IBEW bring a generator to the site just in case we needed it.
On the morning of the event, the company pulls up and I ask them if they brought a generator. A concerned look came over the person I had posed this question to. He responded, "no, I was never told to bring one." I then informed him I had a generator for him and his part of the event proceeded as planned.
The rule of any event is if you don't hear it first hand, don't assume that what you are being told will actually take place. You can NEVER be over prepared!