Designing a kitchen is easy: refrigerator there, oven there, sink and some cabinets. Just need to make sure everything is there and have their own places. There is the kitchen triangle between the sink, fridge and the stove and so on. Sure there are many options but there is finite amount of things that need to be placed and lot of constraint that limit the choices. But that's just the start.
Once everything is in their place in the plan the real work begins. What materials to choose, what colours should everything be. And that's just the overall look and feel of the whole. Then there are the cabinet mechanism (once you have managed to choose between the traditional door cabinets or the drawers. Should those have the pop-to-open mechanism or handles, or maybe the pulley groove on top (or bottom). What kind of handles?
The lighting is also important part of the functioning kitchen. But were the material finishes too reflective? Should there be more indirect lighting?
What about the appliances? What are the must have features? What about the nice to haves that would add that little premium feel. Do these all fit into our budget?
And in the end all these choices should satisfy the both of us.