Here's why:

* Atomic Structure: Carbon has 6 electrons total. Its electron configuration is 2, 4. This means it has 2 electrons in its first shell and 4 electrons in its second 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 Goal: Carbon only has 4 electrons in its outer shell. To achieve stability, it wants to gain 4 more electrons, bringing its total to 8.

This is why carbon forms four bonds, often with other carbon atoms or with atoms like hydrogen, oxygen, and nitrogen.