A legal speed can still be inappropriate. Your speed should match visibility, road conditions, hazards and the space available.
You should make safe progress without exceeding limits and be able to stop within the distance you can see to be clear.
These examples are for understanding and practice; they are not a promise that a particular mistake will always receive a particular grade.
Driving at the limit into a bend where the visible stopping distance is too short.
Missing a lower limit or failing to reduce speed for poor conditions.