In his wonderful book, Watership Down, Richard Adams creates a fictional world of rabbits complete with a culture of folk heroes and tales. He even creates Lapine, the rabbit language. Adams reasoned that rabbits could not count higher than the number 4 and therefore invented the word "hrair," meaning all numbers greater than four.
It would be like a little kid counting, "One, two, three, four, a thousand." The rabbit folk hero in Adams' world is even named El-ahrairah, meaning "Prince with a thousand enemies."
It seems that trombonists have a similar gut reaction when counting ledger lines. In our case, I think basses don't count much higher than three ledger lines above the staff...
..while tenors don't count much "higher" than two ledger lines below the staff...
Especially with high notes, this may cause a problem in which we over-react to the printed notes. We see a note, label it as a high note (with "hrair" ledger lines, oh dear!) and tense up for it.
Many, many times, I have seen a student imitate me and gliss up to much higher notes than those printed in their music. Usually, they aren't aware of what notes they're playing and are sometimes surprised when they discover that they just played a "high C" or "high D" at the top of their glisses.
Even though student X can gliss up to, for example, a high C with relative ease, they might still struggle with the following passage..
They see that A on the second line with soooo many ledger lines below it and the brain might just lock up: "Whoa, that note has like a thousand ledger lines!" Psychologically it may as well be this note:
One would think that clefs would help solve this problem, but they introduce challenges of their own!
I guess this once again boils down to "stimulus-response" psychology and just overcoming that natural tendency to panic a bit as those ledger lines approach. That's why, in my warm-up, I gliss up to an F early on. It helps inoculate me against tension when I see one of those notes with hrair lines below it.
You might say it helps me fight that urge to run away and hide under the ground..