First impressions are often the truest

I quote from William Hazlitt:

First impressions are often the truest, as we find (not infrequently) to our cost, when we have been wheedled out of them by plausible professions or studied actions. A man's look is the work of years; it is stamped on his countenance by the events of his whole life, nay, more, by the hand of nature, and it is not to be got rid of easily.

Basically the way I read this, is that the first impression tells a lot about the person. The experience encountered, the type of attitude. That is why it's always good to make a good first impression.