Sometimes they can be a accurate sign.
But most often they aren't either.
Personally I don't hold first impressions as an absolute, what if the person was having a bad day? what if they aren't always like this and are actually the opposite of this?
Sorry, what'd you say? Now, how do you feel - that's how important first impressions are. they are our survival instinct.
True, ianlarc's is a very good one, but pur first impressions are so tied in with our survival instinct that they don't take into account whether a person is having a good day or not. Really didn't matter if the woolly mammoth was having a good day, as he is chomping your ear off - Tusk Tusk!!
it really depends on that impression. When I first got to know my hubby, I hated him. I thought he was an arrogant jerk with his head up his own backside and he thought i was a snob. However, my first impressions were wrong and thirty years on, we are still together.
I don't make a very good first impression, I might grow on you though! I am parasitic that way :D
They can be .. but it's more important to get to know someone before you decide what you really think.