Proverbs 28:14 Happy is the man that feareth alway: but he that hardeneth his heart shall fall into mischief.
Happiness is God’s promise for the person who believes all the time. On the reverse side, the unbeliever, who has hardened his heart against God, will fall into mischief. This depicts a common black-and-white differentiation between all people. Some people have come to faith in Christ, are saved, have eternal life, and “fear the Lord always.” Fear = believe. The other people do not trust in Christ alone for salvation, remain in eternal death, and have “hardened their heart.” Harden = not believe. The whole world is separated in this black-or-white way: believer or unbeliever. We cannot know the difference for we cannot see the heart, and we are commanded not to judge. So we live in the gray; God lives in white and black. He alone judges.
A more usual Biblical translation for “happy” is Blessed, as in the Biblical declaration: “Blessed is the man who trusts (fears) the Lord.” Blessed connotes many different aspects of goodness, happiness and well-being. We may not always consider our life to be so wonderfully blessed all the time, but it is, according to the promise. God says it; it is so. God promises; it is real. It is abiding and eternal. Eternal Truth is stronger than the present-moment feelings.
The other side: those who ignore, deny, suppress, or remain ignorant of the love and mercy of God, the grace and forgiveness of Jesus, and the presence and power of the Holy Spirit harden their heart. This is unbelief, the primary sin. For them, they shall fall into mischief. A better translation for mischief is calamity. Paint it like it is: unbelief is an eternal calamity. Trust is eternal blessedness.