As odd as it may sound however -- while I truly can relate to all that this article is saying! -- I can also spot Si a mile away. I find it to be a very easy function to pick up on; it just involves listening to what someone is talking about, and how often they bring up memories, or how something relates to what they've previously experienced. Very interested in learning the details of something, also may have a sort of "tense" or "nervous" air to them. Actively seeks comfort.(1) The aspect of your personality that you show people when they first meet you is known as the function that you "Extravert." This describes how people first see you. This is what you present to the world.
Extraverts (those whose first letter is "E") show the world who they really are. When you meet an Extravert, they show you their Dominant function.
But not so for Introverts. A person who has a Type with the first letter being "I" ( indicates they have a preference for Introversion) will not show you who they really are at first. They will show you the function they Extravert, which is not their Dominant function.
This is why getting to know Introverts is a little harder at first, besides the fact they are more quiet and less likely to initiate a conversation than an Extravert.
For example, look at the 4th Personality Type in the list, INTJ. Their Dominant function is iNtuiting. But they Extravert (show you) their Thinking (T) function instead.
All Introverts keep their Dominant function hidden and instead show you something else. Thus when getting to know and Introvert, you have to take more time to look a little deeper and to get them to talk about what is really important to them.
Extraverts are much easier to get to know because they will usually be talking about what is important to them.