I am going to quote uusu from reddit forum
"Welcome to the culture of Estonia.
Please avoid any form of eye contact with people you haven't met before. Even then, keep it at a minimum and try to ignore anyone who isn't in your circle of 3-4 best friends. In case of accidental eye contact it is most important that you turn your whole head away immediately.
If you talk to your Estonian friends, don't hold eye contact for more than 2 seconds straight. Eye contact longer than 2 seconds, even when talking one on one, will make the average Estonian very nervous. The longer you stare, the more agitated the Estonian becomes. These are the internal thoughts of an Estonian when you're talking to him and staring straight in the eyes: "Damn he's one of those starers. How can he stare so long at me? Why is he doing that? Is he trying to dominate me? I'm bigger than this! I can stare too! Damn, I only managed a second or so. He's still staring. I'm totally confused and don't really know what he's talking about. Is he a serial killer? He must be a rapist."
You don't just say hello to the Estonian. You need to have a reason for it. Seeing a friend? Say hello to him! Don't say hello to his friend though, you don't know her. In the check out? Say hello to the cashier. If an Estonian says hello to a cashier, he feels like he's had enough socializing for the day. Though when confronted with a colleague in a corridor walking towards him who he doesn't know so well, he can say tere, but he doesn't really have to. He's in much safer hands pretending he got a phone call on his mobile. Or easier yet - he just looks at the wall and pretends to be in deep thought. Now he escaped a possible social contact event."
Well yea we like to keep to ourselves but once you get to know somebody they usually open up :)