The concept you're referring to is known as the law of conservation of energy, which states that energy cannot be created or destroyed in an isolated system. This principle is a fundamental concept in physics.
However, matter can indeed be converted into energy through processes such as nuclear reactions. This is described by Albert Einstein's famous equation E=mc², where E represents energy, m represents mass, and c represents the speed of light in a vacuum (a very large constant).
According to this equation, mass and energy are interchangeable. In certain circumstances, when matter undergoes nuclear reactions, a small portion of its mass can be converted into energy. This process is most commonly observed in nuclear power plants and in nuclear reactions such as those occurring in the Sun.
Furthermore, in everyday situations, matter contains enormous amounts of energy in its atomic and molecular bonds. When these bonds are broken or rearranged through chemical reactions, energy can be released or absorbed. This is the basis for various energy transformations, such as combustion, digestion, and cellular respiration.
In summary, while energy cannot be created or destroyed, matter can be converted into energy through nuclear reactions, and energy can be released or absorbed through chemical reactions involving the rearrangement of atomic and molecular bonds.