the ideal path through a product is usually easy to draw. the harder work starts when someone arrives with the wrong file, an expired session, a slow connection, or a question the interface did not anticipate.
i want to design for those moments early. a product should explain what went wrong in words a person can use. it should protect their progress where it can and give them a clear route back.
failure states are not edge decorations. they are part of the experience people remember because that is when they need the product most.
the real test of a flow is whether it still helps when a person does something unexpected.