The first three verses of Deuteronomy 13 warn against believing false prophets. More to the point, they warn against trusting in circumstances. Moses commands that even if a prophet predicts something that comes to pass, that does not immediately mean they are to be trusted.
It is an important teaching for us today. We tend to trust our imperfect perception of circumstances. If something happens we like, we should not assume it is God blessing us. If something happens we don’t like, we should not assume it is a punishment. Our feelings about a circumstance should not dictate our belief.
Moses warns us to make choices based on what is true. Our trust, our reverence, belongs not in the manifestation of particular circumstances (finding a spouse, getting rich, etc.) but in The Lord.
If we follow our circumstances, we will follow a false prophet. A promise that happiness lies just beyond a circumstance, like riches or relationship, is idolatry.
If we have the courage to follow the Lord, we will find him faithful and true in all circumstances, including trials. True success is more complicated, more transcendent than our emotions. It only comes through faith, placing our trust in the one true good, The Lord Jesus Christ.