Let’s say that

Carlo is a very cultured man, he is often invited to talk about astronomy in front of an audience. Carlo is also a shy man and during his lectures he often repeats, between one speech and another:

Let’s say that…

Boy raises his hand to ask a question
A little boy asks a question

At the end of the conference, Carlo asks if there are questions from the public. A little boy gets up and asks him:

Why do you often repeat “let’s say that”?