The classic introvert watches and listens.
Introverted people are not as talkative as extroverts and also value spending time on their own.
That means you simply won't see them as often as extroverted people who want frequent social stimulation.
If you've got a crush on an introverted person, how are you supposed to tell if that person likes you back?
How do introverts flirt if they are quiet and absent half the time?
You're going to have to pay close attention to figure out if your stars are aligning with the object of your desire.