Social engineering is manipulating a person into doing something against their own interest. It is the common ancestor of phishing, impersonation, romance scams and fraud calls, and it works on a small number of predictable psychological levers.
Pretexting is the invented scenario that makes a request seem reasonable. It is the part of a scam that happens before any message is sent, it is illegal in several forms, and it explains why the best attacks ask for nothing at first.
Almost every scam contains a deadline, and the deadline is rarely about the story. It is there to remove the interval in which you would have checked — which is the only interval that matters.
Police, tax authorities, immigration, the courts. Authority scams work because compliance with legitimate authority is a trained reflex, and because the threatened consequence is severe enough to override the impulse to check.
Romance scams are patient. The relationship is built genuinely over weeks or months before money is ever mentioned, which is why victims are not naive — they are in a relationship that was manufactured to be real to them.
Imposter scams have been the most-reported fraud category for nine consecutive years. The impersonation itself is rarely sophisticated — what makes it work is arriving at a moment when the story is plausible.