Given a new problem, an experienced programmer often recognises it as a variant of something known - shortest path, or a scheduling problem - rather than inventing an algorithm. Why is recognition so much more productive than invention?

C. Because a recognised problem brings a proved algorithm with known limits.

Recognition brings a proved-correct algorithm, a known complexity, known edge cases and usually a tested implementation; invention means taking all of that on yourself. The mapping step is worth practising, 'assign staff to shifts' is bipartite matching, 'order tasks with dependencies' is topological sort. Recognising a problem as NP-complete is valuable too: it tells you to stop looking.