Being a natural introvert is hard, especially when society is made for extroverts.
1. The mental dilemma of whether or not to say "Hi" to that person you "kinda" know.
You don't know whether or not to say "hi" (or smile at) to your friend's roommate/sibling, that girl you have mutual friends with but haven't officially met or that person in your class who sits next to but have never talked to before. The thing is: You know who they are AND they know exactly who you are (you're absolutely sure of it). So it becomes an everyday struggle when you pass these people in public. If you spot the person coming towards you, you get about 10 seconds to decide if you are going to greet them or pretend you're lost in thought/on your phone/listening to music/etc. and then about 2 seconds to execute your greeting or to strategically time pulling out your phone like you got a text.
2. Having "friend-crushes."
A "friend crush" is when you want to become best friends with someone who doesn't know you well (or at least not well YET). You have a feeling deep down that you and this person would be amazing friends once he or she gets to know you better. If only you could get over your shyness quicker...
3. The constant need for alone time.
If you don't get the necessary alone time to "recharge" you start to go crazy. Being around people for extensive periods of time is draining. You're always amazed (and sometimes even envious of) by those people who can keep talking to people for hours on end without any break. You hardly ever mind walking to class alone or doing homework by yourself. It gives you a chance to think things through, take a break and be with yourself.
4. Overthinking EVERYTHING.
Introverts tend to think about everything. They extract meaning and analyze things that were said to them or experiences they went through that day. Introverts often pick up on subtle body language or the tones of voice when you interact with them. They'll even pick up on little things and remember how you treat them. They hardly ever forget these experiences and will carry them around inside their mind until its necessary to bring them out again.
5. Being misunderstood.
A lot of people can mistake your quietness as a sign of insecurity, lack of personality, or even rudeness. However, this is hardly ever the case. For introverts, it's hard to relate to people who aren't because they don't fully understand what it is like to be naturally shy and how shyness influences the way we perceive the world around us and thus our outward actions.
