It's more common to quote Proverbs 3:5 with verse 6 as well. Verse 6 isn’t possible without verse 5, but our focus is almost always drawn away to the good news verse 6 provides. 

Verse 5 tells you to “trust in the Lord with all your heart.” The only way to trust God completely is to “not lean on your own understanding.” It's a spiritual discipline to learn to trust God as we are called to do.  

Remember that in ancient days people understood that the heart was the “driver” of a person’s life. In Scripture, the heart is often associated with passion and motive. God wants us to trust him above all other motivations. We are to trust that only God’s motivations are completely pure; therefore, we should trust him more than any other. When we understand God’s motivation is pure, we are more likely to trust his will.  

But trusting God stands in conflict with most of what we are taught and, truthfully, what we teach. We know it's important to “think for ourselves.” It's important to gather the facts and process them into a well-thought decision. Yet, Scripture tells us not to lean on our own understanding. 

God created us, and his word encourages us to be “thoughtful” in our actions. God gives us discernment and good judgment through his Spirit. God will never contradict his word, yet a lot of our decisions and choices aren’t directly addressed in Scripture. A key to Proverbs 3:5 can be found in the word leaning. 

When we lean on someone, we trust them to hold us up. When we lean a ladder against a wall, we trust that the wall won't fall. We don’t lean on something we know is weak or flawed. That is why we are to trust God with our whole heart. God can never be untrustworthy, weak, or flawed. God holds us, his children, in his righteous right hand. The same hand that created the world is able to do all things, all the time. 

Then, as Proverbs 3:6 says, “you will acknowledge,” or know, God. Knowing who God is through his word makes it possible for him to “direct your path.”  

Allow the word of Christ to dwell in you richly and you will likely learn to lean on it more than your own understanding.