For me, the possibility of external influence on behaviour, means that we must be careful to conclude that tjhe reactions we see within ourselves or happening to others are always results of gati. Maybe this is mostly true, it may not be true in a particular situation.
I think i experienced something external at least one time, when i felt a strong urge to harm myself very badly. It felt strange, as it was not gati. It felt alien. I became cold that moment. I survived this ‘attack’.
It would not surprise me if a lot of people are influenced externally.
I have heard that paranimmita-vasavatti deva’s can take control over and, for example, stimulate people to act sexually, so they as deva’s can enjoy that.
Also creation proces can be very obsessive, forceful. Writers, poets, painters, artist, know this. It can be like one is possesed. Maybe this is not far from being true.
Siebe