I think any kind of relationship between two people can be evolved once both agree with that. There's a popular proverb that says: "it takes two to begin a fight".

I don't really think so.  Colleagues are and are termed as colleauges, while friends are and are termed friends.  They are different to me.  There might be an inbetween, but I'd rather keep them 2 completely different groups of persons, which I don't mix up.  

For me, real friends are my shelters, where I can be who I really am and do not need to put on any façade.  Friends like you for who you are, while colleagues would sometimes pretend to like you just for sake of work. Friends would forgive your being silly, while colleagues would not do so easily.  But it is always good to be friendly with colleagues.

 Here too in France, friendship between colleagues is very common. They will see each other after work too etc...There are many many good friends and colleagues :)

Well, you know life.

Most of my parents' friends are/were colleagues. A lot of my dad's friends are people he works for or people who work for him. Just about everyone where I work are friends with each other as well, and a lot of them party together after work. I know several of my sisters' friends are colleagues as well. I didn't know this was so uncommon outside Australia.

Alexander,

I said this because it is necessary  to make sure that friends are really good. Otherwise some are talking too much and repeat some parts of your private talk to anybody and others are manipulative.

Elena,

I think you are not obliged to choose between good relationships with your friends and your career. You can have both.