Some people, they remind you about someone. Their height, their skin color, their body shape, their hair, their eyes, the way they act.
I walked pass through a guy. His skin color, his eyes, his height, reminded me of someone I knew. I couldn't really remember him, but a glimpse of the guy had triggered my memory that he resembled him, or he was really him. Like, something eats some part of my memory it makes me doubt about anyone I've met or talked to.
Can you miss someone's face? Just, his/her face, can you? Because you think you're losing memory about them bit by bit, in your head. You're losing them.