The first door can be opened to everybody.
The second door can be opened to 30 - 40% of the people you meet.
The third door is only for those who are the closest. (one or two, I assume)
I guess that in this way, you can build better relationships.
I'm a Japanese international student studying in Canada. I am trying to improve my writing skills in English by creating this blog, so if you have time, please correct my English. It'll greatly help my writing. Oh, you can write your comments without correcting my English, but please don't use the space for advertising... ( By the way, my older blog and the Japanese one are here too. http://www.sasakukublog.blogspot.com and http://www.sakunikki2008.blogspot.com ) Thank you.