What does Proverbs 15:15 mean?

The contrast here is about how one perceives their circumstances. This is likely not meant as a comparison between success and suffering, but between despairing pessimism and godly trust. Perspective has great impact on one's happiness (Proverbs 15:13).

The word translated "evil" here is not always a reference to immorality; it can also mean something unpleasant or disastrous. Those who are perpetually "afflicted" are constantly miserable under the weight of their own negativity. They make the worst of every situation. Negative people constantly complain and never see a bright side in any circumstances. They are gloomy, negative, and seem bent on making life miserable for others.

Their counterparts are cheerful people. They may encounter difficult circumstances, but they find a sense of joy, even in adversity (1 Thessalonians 5:18). These cheerful individuals help others by encouraging them. They lift the spirits of their friends and associates. Barnabas was an encourager in the early church. Times were tough for many believers. They had come to Jerusalem from foreign countries and lacked jobs and income. But Acts 4:34–37 tells us "as many as were owners of lands or houses sold them and brought the proceeds of what was sold and laid it at the apostles' feet, and it was distributed to each as any had need. Thus Joseph, who was also called by the apostles Barnabas (which means son of encouragement), a Levite, a native of Cyprus, sold a field that belonged to him and brought the money and laid it at the apostles' feet."

A parallel interpretation of this verse is that even those who are afflicted—burdened with perpetual hardship—can experience constant joy if they maintain a cheerful heart.