Here's why:

* Hydrogen only has one proton and one electron. It needs one more electron to complete its outermost shell.

* Covalent bonds involve sharing electrons. By forming a single covalent bond with another atom, hydrogen shares its electron and gains access to the other atom's electron, achieving a stable configuration.

Think of the simple molecule of water (H₂O). Each hydrogen atom forms one single covalent bond with the oxygen atom.