You may also find on the list a traveling companion whom you meet on a train and share the desire to ward off boredom. You exchange greetings and small talk, or make some observations on what you see and hear during the journey. Within a few hours, you share food and you fall asleep in the same space. The barriers between you start to fall and you see and know about one another what only your household members or close relatives would see or know about you, although you are totally unrelated and you have no brotherly affection for each other.
There is also the coffee house companion, the sports companion, and many other different categories of companions. Your relationship with some of them might last for long until you start calling them ‘friends’, but they are not friends. You neither picked them willingly to be your friends nor chose their companionship, but life put them in your way and burdened you with them. If you do not conduct an inventory of them the way a merchant conducts an inventory of his merchandise then you vet them and only keep the good ones and cast away the bad ones, you would not know down which abyss such friendships lead you. A companion drags his companions down the path he is treading, and they tend to follow his example.