Here's why:

* Electron Configuration: Sulfur has 6 valence electrons (electrons in its outermost shell). It needs to gain 2 more electrons to achieve a stable octet (8 electrons).

* Ion Formation: To achieve stability, sulfur tends to gain 2 electrons, forming a sulfide ion (S²⁻).

While sulfur can also form cations in some rare cases (like S⁴⁺), it's much more common for it to act as an anion.