Yep, I learned this the hard way. I thought meeting customers, selling them on an automated, cheaper version of their current crufty manual system would be so easy I'd barely need to try.
There are always people vested in the current way of doing things. If they happen to be influential, you will have to swim upstream no matter how much better your solution is. Companies are ultimately people, not in the Citizens United sense but in that they are made by people, staffed by people, and you will be dealing with people and all their foibles.
I'd never been more wrong.