Why do Generals tolerate getting grilled by senators?

[William F. Owen]

How can military generals act so professional when senators tell them outright to their face "I think this is a failure, and what you've done here is a failure..." Telling the generals they are doing a "good job" when the hearing first starts, then outright bashing them does not help them feel better...

I suspect (know) that behaving cool and polite while an annoying politician grills you, gets you huge amounts of professional respect from your peers. They look like dicks and you look like a professional.