Simply put, if a central atom has to bond to more than one outer atom, especially if more than one outer atom is different, it has to hybridize.

Why do we hybridize orbitals?

The hybridization of orbitals is favored because hybridized orbitals are more directional which leads to greater overlap when forming bonds, therefore the bonds formed are stronger. This results in more stable compounds when hybridization occurs.

Do orbitals always hybridize?

Hybridization is the mixing of the atomic orbitals in an atom to produce a set of hybrid orbitals. When hybridization occurs, it must do so as a result of the mixing of nonequivalent orbitals. In other words, s and p orbitals can hybridize but p orbitals cannot hybridize with other p orbitals.