15.3The most famous borrowed chord: iv in major

In C major:

IV = F major

F A C

But from C minor we can borrow:

iv = Fm

F A♭ C

Try:

C → F → Fm → C

This is one of the most recognizable borrowed-chord sounds.

Listen especially to:

A → A♭ → G

That chromatic descending line explains much of the emotional effect.