Maybe this is not 100% related but... Having some photography and video background I can say some people( most of them) just can not visualice how a design-edit-retouch will be if they don't see it finished. Even explaining the process that will take place, they are just unable to see how the raw ( or preliminar ) material will be transformed. Even some people with design-art background seems to have problems understanding it if they haven't been fully involved. You have the final product idea in your head and that it is almost impossible to transmit to the client without effectively showing the final result itself.