I tell you flatly that I've never met a SINGLE physicist who has maintained anything of the kind. I did once meet a chemist who said this, and I found it shocking. I have met several laypeople who have held this belief.
I believe that a complete and correct theory of particle physics is possible in my lifetime. That is not to say that a complete and correct theory of anything means that there is nothing left to learn about it, or nothing left to invent with it. In fact, having a good understanding of something is often a prerequisite to doing something really useful with it.