Still (un)certain after all these years

I've been a user interface / interaction / user experience design for over 20 years. After all that time, I still don't feel 100% confident that an interface I'm working on is the perfect interface for the intended users. The place where interactive digital systems meet a range of interacting people is simply too hard to predict. One thing I am 100% sure of... I don't trust anyone who feels they know the right answer after little thought and consideration.