Here's a breakdown:

* Not all stars explode: Only very massive stars (much larger than our Sun) explode.

* Supergiants are massive: They are in the final stages of their life, having exhausted the hydrogen fuel in their core.

* They swell and become unstable: As they run out of fuel, their core collapses, causing the outer layers to expand dramatically, leading to a supergiant stage.

* The explosion itself is a supernova: This happens when the core collapses and then rebounds, triggering a violent explosion that releases immense energy.

So, while not every supergiant will explode, all stars that explode are supergiants before the event.