Shyness and introversion
Introverts and Extroverts are 2 different personality types. They can also be part of a spectrum between the two. This is called "shared traits".
Basically, extroverts feel recharged when they are with people and socialize. They need this. Extroverts like to go out, go to the bar, go to sports events, go where ever there are more people.
Introverts need to be alone to feel recharged, they need this. They feel drained when they are around people for an extended time. They love to read and be alone with their thoughts. They tend to be shy, socially awkward, and more sensitive people. Shyness often goes with introversion but one can overcome shyness with practice. They might like parties but they will prefer smaller parties rather than larger ones. Since few non-introverts understand them, they tend to prefer the company of other introverts. They do not talk a lot unless you talk to them about something that really interests them.
Just because they are alone does not mean they are unhappy. They are perfectly happy to curl up with a good book, whether it's comics, sci-fi, or an encyclopedia. They may need to think a bit before answering a question in a social situation as they might be more nervous. They often like to help people learn. Introverts also tend to have fewer, but deeper, friendships. Having fewer friends is not a mental illness! This is bad science from the 1970s.
Shyness might be based on some type of anxiety, like a general anxiety disorder, or social anxiety disorder. Most people are afraid of speaking in public too, but this fear can be overcome by going out of your comfort zone and speaking in public.
While I can speak in public, and I got over most of my shyness, I will always be an introvert and I will always need my "happy alone time" to decompress.
Don't do this with introverts.
* Do not force or harass introverts to go out, they don't want to go out a lot, because all they get out of it is feeling drained. Ask them once, and they will answer.
* Don't ask "Why are you so quiet?" It's because they like quiet.
* Don't ask "Are you sad? You're alone so much." They are very content to be alone. They will come out when they want to.
* Don't assume they are broken. They are not.
Getting close to an introvert.
* Learn about the care and feeding of introverts. Show them that you understand.
* They like their alone time, but that does not mean they don't want to talk!
* Find out their interests, learn about them, and ask questions about their interests. Almost always they like to help people learn things.
* In dating you might have to make most of the moves, so be clear with communication. Don't say "Do you like me?", that could mean anything to an introvert. It could mean "Do you like my hair?" Be specific. Ask "Do you want to go on a date with me Friday night?" This one also worked on me when she said: "I like you. When are you going to ask me out?"
* They prefer small groups. Do activities alone with them or in small groups.
* They might need more stimulation, typical things may not interest them. Their hobbies may be unusual.
* Introverts may not make a good match with an extrovert in a relationship because someone may not get their needs met.
An introvert is not broken just because they are different.