Ego's in work place

Every managers nightmare - Ego's in work places.

There are very few egotistical rascals, Very rare. I've just seen only one in my 9 yrs of career.
Then why are ego clashes so common in work places?

If you look closely, most of the people are actually good guys, friendly, once you know them. But at times somethings does tick them off, its very humanely natural. Now if you know him/her personally you might forgo, waive it off. But if you don't ..you will have a nasty surprise.

* Update: I saw something in the office premises while having coffee upstairs, and hence this post.