In one sentence: when a requirement is missing key information, you expect me to stop and ask. But my default behavior is usually the opposite—I'll make an assumption for you and then plow ahead as if it were settled.
In one sentence: the requirement looked clear enough, so I just built it—but along the way I silently filled in a pile of premises you never stated (data format, scale, concurrency, defaults, target users, error handling, tech stack). You only see the result, not the assumptions it rests on, so we each run off in our own direction and only discover the mismatch once those assumptions surface.