Presume Competence is the mantra of many AT providers and experts. It is also just good advice when applied correctly.
To presume competence is to never assume that a person can’t do something just because of the way they look, act, or present themselves. The fact that they can’t speak clearly doesn’t mean their thoughts aren’t brilliant – it also doesn’t mean they aren’t listening to everything you say. The fact that they are unable to walk doesn’t mean they can’t move: they may just need some tools.
Learning to presume competence is not always easy: for more on this subject see the excellent articles on PrAACticalAAC.org.