I learned a while ago the hard way it takes 10 times the effort to un-know someone as it does to get to know them and let them in your life, if you find after many weeks they are not good people under the surface.
Discussion
After having known since pretty toxic people in the past few years, is not just my introversion that makes me averse to getting to know people too quick for this reason exactly. A foot in the door is hard to remove.