This is a metaphor I use to describe how I see the delivery/sales relationship in a professional services firm.
I loved The Mad Scientists Club as a child. In one of the stories, the club competes in a balloon race. The final strech of the race is across a lake, approaching a ridge. The finish line is a short distance beyond the ridge. The balloon must cross the lake and top the ridge to reach the finish line on the other side. If the balloon comes into the ridge too high, the strong updraft off the lake will take it high into the air, where there is a prevailing current that will blow it back toward the lake. Too low, and the balloon will not clear the ridge.
By coming in just right, the balloon can clear the ridge, avoid the updraft and land safely. (You can read the book to find out what happens to the kids).
The goal of sales is to increase expectations enough that the potential customer sees enough value in the offering to make the purchase. The goal of delivery is to make sure that the customer gets what is expected. If expectations are too low, we crash into the ridge, and miss the sale. Too high, and we get caught in the updraft, and never deliver the project.
If sales and delivery do not trust one another, it is easy for each to fight over how much to inflate or deflate the balloon. The result is a bumpy ride and its anybody's guess if its to be the ridge or a flight of fancy that is in store. (I am betting against landing safely).
However, if both trust the other, each can ensure that the other's goals are met, smoothly top the ridge and bring the balloon in to victory.
Sales and Delivery are both riding in the balloon. Whether they work together to regulate the level of client expectations, or each fights for its own goals, they cannot escape the fact that they are in it together.