One theory of mine in this respect is that the older you get, the more often you realise you can be wrong, or that there is much more to this than you actually know, so you pepper your sentences with conditionals, and disclaimers.
When I hear some of my young colleagues spouting rubbish but with such confidence, I have to chuckle to myself sometimes. But they're the ones the customers like to speak to because they think they are getting a sound answer. No one remembers me because any answer I give them will be so full of contingencies, based on experience, that they feel they haven't been helped.
My other theory is that we (well, I at least) were expected as children to be "seen and not heard". I can still remember my father yelling up the stairs at us if he could hear us walking around, so we got into the habit of creeping everywhere.
And also, as young ladies, we were indoctrinated to be considerate of others, so we stand back, let people through, let others speak, and unobtrusively smooth their paths.
So - as recommended by JE65, Nonnie, and others in previous posts in this thread, I am going to start from today to assert myself in some little way - at least once a day. The confidence will come with the brashness.
I hope.
No - that's something I shouldn't be saying. I don't "hope" - I "know" and with all the certainty of a millenial. That'll show them!