In his pre-presidential life, Trump was famous for saying, "You're fired!" to people on his TV reality show. But
Trump's firing of acting AG Sally Yates was no reality show. In real life, an AG advises a president on the law, but if that AG refuses to enforce an order that
has been "approved as to form and legality by the Department of Justice Office of Legal Counsel," then a likely consequence would be that the AG could be fired.
The
NY Times reports Yates' motivation this way:
Ms. Yates, like other senior government officials, was caught by surprise by the executive order and agonized over the weekend about how to respond, two Justice Department officials involved in the weekend deliberations said. Ms. Yates considered resigning but she told colleagues she did not want to leave it to her successor to face the same dilemma.
But I would imagine that Ms. Yates understood that her successor would almost certainly face the same dilemma, whether Yates resigned or was fired. And although I grant that Yates and other government officials may indeed have been surprised by the
speed of Trump's executive order, if they were surprised by the content of the order then they hadn't been paying much attention to Trump's campaign.