Making friends sounds easy, but according to my experience, it's not. Firstrly I want to make it clear that, to me, a casual aquaintance like a hi-bye friend is not a friend. It's just someone you met in some occasion like at a party, in a club, in a bar, and you may have a good time with them just for a moment. You may not have a deep conversation with them to get to know about each other. Even when you need some opinions, help, they will not be the right person for you to turn to. A friend is someone who will share his feeling, opinion, trouble, happiness with you, which is based on trust.
How will we trust someone? I think it's based on how much we know about that person. When I'm talking about get to know someone, rather than to know his occupation, his age, etc, I want know about his personality, his hobbies, what dose he do in the leisure, etc. Having those informations I would know if we have something in common, which is important for a friendship. However, the personality and and her way of being are always prevvailed. Does he showed up on time the first time we meet? Is he well-dressed? Is he frank or distrusting? Having thoses imformations, our heart or body can make us the decision without using our brain to think over. That's whay there is someone with whom we know that we will get along well at the first glance.
However in most cases, there're people who won't revail their true personality or they just can't act in their way the first time the met you. People with whom we can get to know well over time. Or that someone you met for the first time and you thought you two would be friend turned out it wouldn't when you knew more about him. There're so much factors that will affect a friendship, such as different routine, different necessity of socialization, the distance, the political stance, living style, etc. Or simply one of you dose not cultivate the friendship.
In my point of view, it's not really hard to make friends, but when it comes to make a true friend, it will be hard, or it's depends on the odds.