Proverbs 3:5-6 “Trust in the LORD with all your heart, And lean not on your own understanding; 6. In all your ways acknowledge Him, And He shall direct your paths”
God requires us to trust Him with all our hearts; but to accomplish that, we need to understand that our own understanding is foolishness to Him. If we are to trust God, we trust Him by faith; which is the substance of things hoped for, the evidence of things unseen. The evidence is not in the things which are seen; it is made up of things hoped for and not seen; therefore our own understanding relies on what is seen or evident at that moment.
There is no hope when we already have something; like you would not hope to see the day when you are in it; however you hope to finish the day and your faith tells you it will end well. But we fail to trust God because we forget to acknowledge He is the one who gives us grace to see the day through. Our own understanding does not guarantee us to see the day through; it does not guarantee us who we will be with or who will depart.
Our own understanding therefore is unfruitful when you have given everything to God. When you have given the day to God, trust Him to lead you in all things, not in some things, but all things.