If you have had an adult family member or friend that was recently diagnosed with a previously unknown developmental psychological disorder (ADHD, autism, etc), you might have noticed something that confused you. Right around the time they were diagnosed, maybe even a bit before, they "suddenly" began to exhibit symptoms when never had before. You might be like, "I've known this person for X years and they never behaved like this." You might even think they are "acting" or something. 1/4