Having a complete front end and back end application where the frontend is designed to look as simple as possible.

A new potential customer wants to have our app and listens to a designer bragging that its just replacing 2 fields.

After a while our manager comes by and mentioned that everything needs to be done within a few weeks....

All devs lose their mind since in the backend we need to have like 8 external sources to connect and hundreds of business rules to implement.

How a single designer ruined the year for 7 devs....