A big reason why narcissists are hard to spot quickly
One of the biggest reasons I believe narcissists aren't detected quicker, in my opinion, is because it is easy for normal people to confuse a lack of empathy for anger issues. We all get upset, angry and even furious sometimes, after all. However, with the narcissist, it is very hard for him or her to control his rage, and so when he blows up, he blows up big time. And this is the trap. His rage is so profound and unjustified that the victim is left confused and then will most likely end up blaming him or herself, thinking that if he didn't mess up, the narcissist wouldn't have gotten so upset.
The truth is, it is nearly impossible to predict what will set off a narcissist, which is why many experts in the field of psychology describe being around one as "walking on egg shells". Now, I brought up a lack of empathy before because for narcissists to be able to treat others in such a dehumanizing way, they would almost certainly have to have a tremendous lack of empathy.
So if you've ever had the unfortunate experience of being shouted at like a lunatic by a narcissist, it wasn't your fault, and you should start to forgive yourself and heal emotionally. It can be done, and I have begun the journey myself with success. Here are a few resources to get you started:
https://blog.melanietoniaevans.com/4-key-stages-of-healing-after-narcissistic-abuse/
https://medium.com/@SoulGPS/10-steps-to-getting-your-life-back-after-narcissistic-abuse-96b5c74af29c