It really depends. Some people have the ability to judge a person from first sight with a high percentage of being right. But I do believe most people cannot do this. Anyway, as the other two already said, I as well do believe that it is really important. We people have some instincts you should not underestimate. They can sometimes save you from harm. But, as Tiago already answered, it is not definetily always. I remember of having an ex-collegue, who told me she was together with someone for 6 years. Then she found out he didn't wanted to have children while she wanted. She told me, if she would had knew this in the beginning, she wouldn't had been together a single minute with this person. But in this way, she wasted 6 years of life for nothing. Another ex-collegue was together with someone but broke the relationship and then he showed his real face. He began to stalk her and even sent death threats to her. Those are a few things you cannot see on first sight, but otherwise you should trust your first sight feelings. If you have the ability, you can already consider a person very close to the truth at first sight and it can help you very much to make the right decisions.

Yes,it's very important,but not definetly was he\she is real. when I meet a person,the eyes are the first place I look to know if she's trustful

Yes, first impressions are extremely important when meeting someone. Here is a quote I like: “My father had taught me to be nice first, because you can always be mean later, but once you've been mean to someone, they won't believe the nice anymore. So be nice, be nice, until it's time to stop being nice, then destroy them.” It's always better to make a good impression first. You never know how important or life-changing this situation/meeting/person could be. If you find no need to maintain appearances later, then be yourself ^^ Making a good first impression isn't about being fake (or it shouldn't be), but about putting forth your best face and being the best version of yourself you can be in order to be appropriate for the situation. Sometimes the first time you meet someone it's so fleeting and/or boring, you forget all about each other and the second time you meet you might really be making a first impression haha