Why is there pressure behind only one of your brakes and not the other?

Pressure behind only one brake can occur due to several reasons, such as a malfunctioning brake line, a leak, or air trapped in the braking system. If there's a blockage or damage in one brake caliper or line, it can lead to uneven pressure distribution. Additionally, issues like a stuck piston or uneven wear on brake pads can also contribute to this problem. It's crucial to address this issue promptly, as it can significantly affect vehicle safety and braking performance.