One professor divided the students into several groups, sent each group some jigsaw pieces, and timed to see which group could be completed first. In fact, the numbers are marked on the back of each puzzle in order, and only need to be stitched in the order of these numbers You can spell the whole picture very quickly, but very few groups notice this. Some spells a long time before they find the digital mark on the back, and some never see it at all. What does this text mean? ['Careful observation is more conducive to success.', 'Pay attention to the pros and cons to fully understand things.', 'Opportunities only for those who are prepared.', 'Sharpening the woodworker.']