Familliar face or total stranger?

Yes, it's finally CNY! Yeah well I know I should be doing my homework but whatever... Time seems to fly by like duper fast. Sometimes you see someone you recognise but if you look closer, you realise there's so much you do not know and that person then feels like a stranger. It's just this weird sensation I get occasionally like you do not realise how tall your baby cousin actually grew until you look carefully/measure his/her height and you start wondering how long ago was she only just as tiny as you could imagine considering the fact that humans differ so much from when they were infants as compared to, say, goldfishes (not including the time when they were eggs, maybe I should try guppies since they give birth to their young...). Eh, I think what i'm writing about now is utter crap but anyway, try this, think of a person in your family or group of friends and try naming their favourite colour, half the time, we don't get it right unless we actually do ask everyone for their favourite colour (Just for the record, mine's dark purple, wait no, black, uggh, i have no favourite colour...). Sometimes we even forget their surnames... Just a couple of moments ago, I was starring into my cousin's face and realised how much she has changed. I was completely clueless as to what to say, we were just so awkward around each other. Although I do see her almost every weekend, now, we mostly just smile at each other, you know, there really isn't much to say. Last time I met my friend at a class reunion, I thought "yes, i know her name but who is she?"
So do you really know the people around you or do you not? What does it mean to know someone anyway? Is it just to recognise them or to really understand them? What is the difference between recognise and know? Or is there no difference?
Perhaps everyone we think we know, actually, we do not.