Do not be wise in your own eyes; Fear the LORD and depart from evil. It will be health to your flesh, And strength to your bones. Proverbs 3:7-8 (NKJV)
Being wise in your own eyes means having more confidence in what your reasoning and feelings say than what God says. Evil is not only the obvious like murder, adultery, robbery but every way of thinking and acting that contradicts what God says. When Jesus told a man that his sins are forgiven, some people questioned it in their minds and Jesus called that evil thinking – Matthew 9:2-4. Most of the time our senses contradict what God says and that’s evil – Romans 8:7
Departing from evil is choosing to put what God says above what we think or feel. This is life – Romans 8:6. This is what brings health to our flesh and strength to our bones. For example, when God says with long life He satisfies you – Psalms 91:16, choose that above what nature and science say that your life expectancy is already determined by certain physical, geographical, and social aspects. When human experience says that the older you grow the lesser your strength, reject it by choosing what God says that as your days so shall your strength be – Deuteronomy 33:25.