Thinking of others...

So why is it that there are so many people out there that don't think of others? one example of what i am talking about is.. just the other night i went to dinner with some friends to this indian restuarant. we were celebrating our friends' engagement. and even my L mentioned that there isn't a lot of food should we order more. and noticed that by the time that i got the sea bass there was only this tiny piece left with a whole bunch of juice/sauce.. keep in mind that my hubby still hasn't got any. so i said that since he has chicken to eat i will take this.. but he gave a look.. so L gave me some of her's to eat.. and i just gave him the fish and was about to ask if he wanted more and he just wasn't happy with me. and said look over at M's plate (which is L's boyfriend).. so i take a peak and notice that he has a mountain full.. and hubby's is not even have full.. so why is it that while knowing that the amount of each dish isn't a lot that some people take more then their share? is it because they think they won't get enough so they want to take more? not thinking that the unspoken rule of take a little and let everyone get a piece. once that dish goes around you can take seconds.