Adversity means a time of testing or a time of trouble. The writer of Proverbs uses what I often call the biggest word in the Bible-if- to indicate that when you are faced with adversity, the outcome could go more than one way. The onslaught of trials, troubles, and tribulations doesn't mean that you automatically lose. You actually could come out of the problems better off than you were before. You can succeed regardless of the adversity- or you can fail- it depends on how you handle yourself.
According to this Scripture, failure is the outcome when your strength is small. The Word is not talking about physical strength or mental strength; it's talking about a lack of spiritual strength. If strength can be small, it can also be big. How can you become spiritually strong? The same way that muscles in your body become stronger- through exercise! Spiritual strength can be increased through exercise as well.
If you've been weak, you can be made strong. If you are strong, you can be stronger still. Exercise your spiritual muscles daily by speaking the Word of God and praying in the Spirit. When you pray in tongues, your spirit gets built up. When you speak the Word, you faith grows, your joy increases, and you become strong in the Lord. Build up your spiritual strength so that you will not faint in the day of adversity!