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Lol. A good guess.

Seriously most people are simple people and if you know a little about that person you will probably get really close. Most people have a birthday in a code somewhere, maybe an important date like an anniversary.

I can recall someone in the Army who had a pin for his bank card as 123456. Things have moved on since then but it shows you how some people think. These days some passwords need lower case, numbers etc so it is not straightforward but some sites don't and those are the ones that could be at risk.