A supernova is a powerful explosion that occurs when a massive star reaches the end of its life. The star explodes, releasing a large amount of energy and matter into space.

There are a few reasons why a supernova might not explode.

* The star is not massive enough. A star must be at least 8 times the mass of our Sun to produce a supernova. If the star is not massive enough, it will not have enough energy to explode.

* The star does not have enough iron. Iron is the fuel that powers a supernova. If the star does not have enough iron, it will not be able to produce enough energy to explode.

* The star is too far away from other stars. Supernovas can be triggered by the shock waves from other nearby supernovas. If the star is too far away from other stars, it will not be able to receive the shock waves that it needs to explode.

If a star meets all of these criteria, then it will eventually explode as a supernova.