I suppose it could be but not necessarily. The instances I've witnessed have been where there is an imbalance of power.
Very True.... I AM a PA, and power was certainly a trigger for me. The higher the imbalance, the more likely I was (still am, but working on it) to be a PA.
Power, multiplied by the intensity of the request. In re-reading and thinking back, I do remember a time when I was asked, on relatively short notice, to take a friend of my wife to the airport. (btw.. the friend asked me directly, and, I frequently go there on my own as I travelled extensively for work at the time).
I had already made another commitment for the time in question. My PA instincts told me to say 'sure.. no problem' (knowing fully well that it would be impossible to do so, but, the **** would hit fan at a later time)..... but.. because the power situation was relatively even, and she was almost apologetic for asking me, I was able to say 'I have already existing commitments, so I have to say no'.
Had it been my wife, or one of the ex bosses I have dealt with (relative power), and the request came in as an order(intensity of request/demand} ... I would have said.... sure, no problem.... and then, when the time came, missed that with a stupid excuse, seriously pissing them off, or failed to show on the other appointment.
The mantra is 'It is ok to say no, it is ok to say no, it is ok to say no'...... it is work in progress.