Like all video game engines, when your game runs, Unity is executing a giant loop, repeating over and over each frame update. Unity provides many hooks to tap into events at just about every step in the game loop. Depicted below is the life cycle flowchart, taken from the Unity Manual page Execution Order of Event Functions (https://docs.unity3d.com/Manual/ExecutionOrder.html). The two event functions you are most familiar with, Start and Update, are highlighted with the red arrows. The green dots highlight a number of other events we'll reference in this conversation:
Starting at the top of this chart, when ...