What 2 ways can air get into a hydraulic brake system?

Air can enter a hydraulic brake system primarily through two ways: first, through leaks in the brake lines or fittings, which can create a pathway for air to infiltrate. Second, during maintenance procedures, such as replacing brake fluid or components, if the system is not properly bled, air can be introduced into the hydraulic lines. Both scenariOS can lead to decreased braking performance and the need for proper maintenance to ensure the system is sealed and free of air.