In this quick Unity tutorial, I break down two tiny-but-powerful MonoBehaviour callbacks: OnEnable() and OnDisable(). These are built-in methods Unity calls automatically when a GameObject becomes active or inactive—so you don’t manually invoke them. I explain when each one fires (scene load, SetActive(true), and SetActive(false)) and why they feel like part of Unity’s event-driven system: Unity watches the object state, and the moment it changes, these callbacks run. To make it super clear, I code a simple color-changing example using a Renderer reference. I grab the Renderer in Awake (small correction from Start—Awake is better here because I want the component ready as early as possible), then I use OnEnable to turn the object green and OnDisable to turn it red. I also show what happens when you click the object with OnMouseDown: I deactivate it immediately (triggering OnDisable), then use Invoke to reactivate it after 2 seconds (triggering OnEnable again). The big takeaway: even though disabled objects don’t render and won’t run Update/physics, OnDisable still runs right before it disappears—making it a perfect place for cleanup, saving data, or stopping effects.