The Good
They have a deep, thoughtful nature which works well for philosophical discussions.
They are a natural option for helping problem solve. They tend to want to solve problems and are a great foil for bouncing ideas.
They typically have a dry, dark and/or sarcastic sense of humor.
They keep you honest. They are very determined to not fall for charms. If they aren’t doing something, you are not going to convince them with smooth talking. It can be freaking annoying, but they will call you out occasionally. This is good if you are the type of person that likes to be pushed and don’t hold grudges.
Their independent nature is a godsend. They have no time for small talk, and know how to focus. They are perfectly okay being in a room with someone and not talking at all. They do not get upset if you too are busy.
They are great friends. Loyal, reliable – they are always there if you need them. INTJ hugs are the best, even if they are doing it because they know that people tend to stop being annoying and emotional if you hug them for a while.
The Bad
They are stubborn. If they aren’t doing something there is no way to make them do it. If you push too hard, they will actively rebel against it. Even if it is not in their best interest.
Tendency to overthink. They think through everything so that they can have the most elegant solution but sometimes you they do this even when the task is trivial.
They want to be in control. Not in charge, in control. Some INTJs just want the illusion of control over their own lives. Some are downright controlling.
They tend to think they are the smartest person in the room. They don’t trust others to do things correctly, so when they are in a leadership role they end doing much more they necessary because they don’t trust others enough to delegate.
They tend to think they are always right. They will purposely ignore what you are saying because they have already decided what you were going to say and have discounted it.
They are set in their ways. Get up. Have a cup of coffee. Eat breakfast. The whole routine takes an hour. They oversleep – it still takes an hour. They will eat the same thing for breakfast and lunch, even dinner every day. I know saving brain power for important thinking. This means they also might not be comfortable with new things.