The business of friends can be a joy or a major disappointment. Disappointment can be avoided with the right attitude and expectations. There's a whole class of people we'd all call "Strangers." Most strangers are already well equipped with friends. They neither need or want more. That's why relocation can be so hard. Everybody is all friend-ed out. When it comes to strangers the best policy is a smile and apply polite consideration. Hold a door open for a stranger. It'll brighten their day and may even result in them being nicer to another person. Now there's a contagious disease that's worth having and spreading. If you're caught on some dark out of the way street in a place like New Orleans, a brisk pace toward the nearest and brightest light might be a better path to take. Strangers are better dealt with in in well lit public places. Friendly and foolish both start with "F" but the similarity ends there.
I find the whole friend thing is best approached with a simple classification system. True friends are a rare commodity but perhaps that's a good thing because giving of your self is key to that relationship. Those that many would call friends are what I call acquaintances -- nice to be with when you see them but interaction with them is by accidental proximity. They help make day to life more pleasant. Depending on them to be true friends is a path to disappointment. Engineering extended proximity with an acquaintance won't make them a true friend it will turn them into someone that's wants to be a stranger.
The next group, hopefully smaller, is the SOBs. Bad mouthing those not within ear shot is a clear indicator of the well practiced SOB. They are often very destructive to our career. The worst SOBs, enemies, can't wait to stab you in the back. Another accidental proximity class. They can be avoided except at work. I've never found a good answer to this problem at work. The best you can hope for is steer them to self destruction. Once achieved though many will fear you'll do the same to them and forward motion in your career comes to a stop. The enemy is an SOBs that seek you out. They consider a smile and respect of others a weakness to be exploited. Smile anyway they also consider your smile a threat since they can't come up with a real smile. There's always one or more lingering around.
Lastly is the small special group of true friends that think about you and are there when you need them. They make life good even when it is otherwise bad. Don't expect to have many. Many true friends come from our childhood -- those we went to school with. True friends deserve an investment of our time and mind share. They will do the same for us. In all my years of work I've met many people I liked but added few true friends. Cherish these few because they are more meaningful in our lives than all the rest.