A single screen can be beautifully designed while the flow it sits in is broken. Flow problems — unnecessary steps, confusing branching, dead ends, missing confirmation — are the most common and most damaging category of UX failure. They are also the hardest to see, because they only reveal themselves when you observe someone moving through the full experience, not when you evaluate individual screens in isolation.
Mihaly Csikszentmihalyi's concept of flow — the psychological state of complete absorption in an activity — gives us a useful metaphor. A well-designed user flow creates the conditions for cognitive flow: the task demands match the user's capability, feedback is immediate, the path forward is always clear, and interruptions are minimised. Flow breaks cognitive flow.
User flows should be designed before wireframes. The question of what steps are necessary, in what order, with what decision points — this is the architecture of the experience. Visual design applied to a poorly conceived flow will not fix the flow; it will make the problems prettier. The sequence is: user goal → flow → wireframe → visual design.