I help with tech setup for a number of musicians, bands, and live performances. Equipment is rented far in advance of the show.

Client: Can we have another microphone for the bassist to sing into?

Me: No, sorry - you sent us your tech rider with exactly how many microphones you needed on it. We didn’t bring any more than that.

Client: Oh okay. What about a microphone for this extra guitar amp we bought today?

Me: Same problem.