The core ingredient of our game is the racing bike. It's the entity in our scene that changes states and updates its properties the most often as it's under the player's control while traveling around the world and interacting with other entities. It has several dependencies to manage, such as the main camera that follows it and the HUD that displays its current speed.
The racing bike is the main subject of our game, and many systems must observe it so that they can update themselves when it changes states. For instance, every time the bike collides with an obstacle, the HUD must update the current value of the shield's health, and the camera displays a full screen shader that darkens the edges of the screen to showcase the diminishing endurance.
This type of behavior is easy to implement in Unity. We could have BikeController tell HUDController and CameraController what to do when it takes damage. But for this...