Day-to-day, good PMs will be asking 'why' as much as my six-year-old son does, which is a lot.
Relentless curiosity trumps knowing all the answers
Craft → Product Sense
One of the traits that I look for in PMs that I hire onto my teams, and also when I think back to the people that I've learned a lot from working with over the years, one of the common behaviors or traits is relentless curiosity, this insatiable desire to understand things and a lack of fear in admitting when they don't understand things and being uncompromising and getting the answers so that they do understand.
I would say this illusion that you have to be all-knowing and super confident sets you up to be in a place of advocacy instead of inquiry.
If you listen and you know where to go to get the answers, that in itself is like a tremendous place to be.
My goal there is not to annoy the person, but it's to understand the content.