Pride cannot trust God. The posture of trust is too weak. It calls too much attention to the strength and wisdom of another. Trusting God is the heartbeat of humility, the opposite of pride. The other is that we realize that we cannot guarantee our security, and so we feel anxious.
Pride is anxious about the future.
I, even I, am He who comforts you. Sounds strange doesn't it. But that's how subtle pride is. Pride is the root of our anxiety. Casting your anxieties on God means trusting the promise that he cares for you and has the power and the wisdom to put that care to work in the most glorious way.