The negative thoughts might be right, but CBT is a tool to help a person figure that out. You work on removing a negative bias from your thinking, and if it still makes sense after that to perceive something as negative, than you do, but before deciding that, you’ve removed things like catastrophizing, paranoia, grandiosity, etc.

It’s not meant to delude yourself. It’s meant to give clarity to appropriately assess the situation and act accordingly.