You learn things right after you need to know them.
Older people, especially those with reputations as being important people, are scary.
So when I deal with an 'important', older person they don't meet me. They meet me scared.
And on the phone is worse.
Later Edit: After you've hung up it's hard to call again and say, "Yeah, I really should have been more assertive and I'd like to ask you to clarify x and give me more info on y, and I have a perceptive comment about z that may change how you look at it."