I checked my mirrors, and it was all clear. Because I was so certain that there were no cars coming from behind, I didn't even bother to turn on the turn-signal, I just swerved and changed the lane. And then a blast of loud air horn struck me from behind. BAAAAAAMMMM!!!!! Holy shit, where did THAT come from?!! I jumped in my seat and swerved back to my lane. My heart, bouncing like a rabbit. Cold sweat poured out of my pores... holy crap... that was close... -- It is when you are certain, that you should be cautious... for the certainty makes you go blind... and the unexpected shit is going to hit you from the blind spot. The more certain you are, the more blind you get. So the more certain you are, the more careful you should be. -- Do not rely on just looking at the mirrors, always turn your head around to check the blind spots behind your car when you change lane.