It allows an average time of one hour to solve a national-level olympiad problem. For ICPC, we are expected to solve each problem in 30 minutes. Codeforces wants 15-20 minute time is reasonable for each of their problems.

Why do we need to solve problems very fast?

1) Because the world is moving very fast, so are we?

2) Because there are many good men, so we must use timing as a way to classify the level of contestants?

3) Or other technical reasons (like decreasing the cheating in the contest)?