Why some people begin every sentence with the word "So"?

I like the answer about discourse markers but I would also add that the word "so " or "so OK" to start a sentence is juvenile or immature. Kids tend to imitate what everyone else says and they all talk alike until they become more mature and they don 't need to use meaningless words to cover their lack of meaningful things to say. Older people may use words like "so" to stall for time to think of what to say next. A more elaborate device in interviews is to reply to every question, "That 's a very good question, " probably while desperately thinking of how to answer.

All languages have "discourse markers" ( http://en.wikipedia.org/wiki/Discourse_marker ) - nominally meaningless phrases that actually convey various meanings such as "I'm starting a new idea", "I haven't finished yet" or "I'm changing topic".

The standard ones change with time, and "So" just happens to have become currently popular as an introductory marker.

Seamus Heaney very nicely translated the opening "Hwæt" in the Old English epic Beowulf as "So":

"So. The Spear-Danes in days gone by and the kings who ruled them had courage and greatness"

It can often be a word used instead of "as a consequence".

It ties what they said before with what they are saying next.

Maybe they are the same people who do not know the correct way to phrase a sentence in English.

If you want to hear something worth listening to, why are you tuned into talk radio at all? :)

So, why do you ask?