The father wanted to teach his four sons not to judge things too quickly based on a single season. He sent each son to look at a pear tree in a different season. The first saw it in winter and thought it was ugly. The second saw it in spring and thought it was promising. The third saw it in summer and thought it was beautiful. The last saw it in fall and thought it was full of life. Their father explained that each was right because they only saw one season, and a tree's or person's essence can only be measured after all seasons. The moral is not to let the pain of one season destroy the joy of the rest and to persevere through difficulties for better times ahead.