The unbelief chooses to believe their own perceptions and intentionally choose not to trust God.
Unbelief will cause you to intentionally dismiss God’s power in favor of your own abilities.
Lord, I believe in You. I will not choose to believe what I perceive with my senses over what you have promised. In Jesus Christ’s name. Amen.
So we see that they were not able to enter, because of their unbelief. (Hebrews 3:19)