In contrast, coming right away with the full, expansive vision is like trying to park a 20-meter-long bus in a crowded car parking lot. There is no readily available space big enough, so you end up crashing into other parked cars trying to force it to fit.
The bus is representing too much of a big vision. it's too big of a pitch covering too many areas that run the risk of conflicting with things the customers do or have or will do. This overcomplicated approach causes collisions - unwanted objections, delays and conversations better had once already working with the customer. They are not yet convinced of the value of enduring a painful parking process.