How many concepts and how many changes are acceptable to the industry?

I would love to hear from other creatives what their agencies deem to be an acceptable norm. I think it is an incredible waste of resources to be doing things over and over and over again. Any attempt to get a coherant brief falls on deaf ears. So how do you prevent the situation repeating itself? And how do you keep creatives motivated and stop them from becoming incredibly frustrated in a system that won't hear the creative need for a brief with a proposition?