Here's why:

* Combustion: Burning is a chemical reaction called combustion. It involves a rapid reaction between a substance with an oxidant, usually oxygen.

* Energy Release: Combustion releases energy in the form of heat and light.

* Oxygen's Role: Oxygen acts as the oxidant, combining with the burning substance to create new compounds, like carbon dioxide and water.

Think of it like this: You need oxygen for a fire to burn just as you need air to breathe.