Here's why:

* Carbon's Electron Configuration: Carbon has 6 electrons, with 2 in the first shell and 4 in the second shell (its valence shell).

* Octet Rule: Atoms tend to gain, lose, or share electrons to achieve a stable configuration of 8 electrons in their outermost shell (the octet rule).

* Carbon's Sharing: To achieve a full outer shell, carbon needs 4 more electrons. It accomplishes this by sharing its 4 valence electrons with other atoms, forming covalent bonds. This allows each shared electron to count towards both atoms' outer shell.

This is why carbon forms so many different compounds, as it can bond with itself and other elements in various ways.