That only holds true up til the point where your loud (public) ambitious goals are the reason for ticket sales.
Once there is financial motive for setting ambitious goals, you lose credit for the ambition -- it becomes driven by profit.
SpaceX is literally taking queries for the sale of private Mars tickets[0].
I have a hard time considering the sale of tickets to a now-technologically-impossible-future-event that may be possibly hundreds of years away from our present time as altruistic.
If I made a website and sold tickets to the "Nicest place to sit and observe the apocalypse when it occurs." for hefty profits i'd be driven out of town. No way I could know where that might be or when it might occur; the entire premise is faulty.
A guy launches a rocket or two and suddenly his opinion, against the majority of the rest of science and engineering by the way, claims we're going to Mars soon.
Sure, he's more believable than some random person saying it, i'll give you that -- but the promise of Mars is something that I and many others consider to be so unlikely in the immediate future that we view the promise as akin to a lie or fraud; and Musk has done little to assuage the very real technical fears behind the mission other than with vagueties like "Well, it's an engineering challenge." or "We'll have to discover new ways of doing X".
Yes, that's true, new method and procedures will inevitably need to be developed -- but dismissing such feats as minor is not only in poor taste, but short-sighted when trying to plan a timeline for when these events may occur.
I think this shortsightedness is intentional, and for profit. He can claim the world, profit from it, and deliver very minimal results that are nothing compared to the promises.
You see this behavior over and over in the management of early Tesla, too.