True, but not always the case. My high run is a 12 pack on a barbox. To do that, I was completely in the zone. While aware of each rack, the number meant absolutely nothing to me at the time. I would say most high runs, the player was in the zone at the time. When not in the zone, yes, the number can very easily cause one to miss due to the pressure of trying to break their high run.
Incidentally, my high run was unfinished. The guy quit me. That was a one time event. I wish I could get back in the zone like I was that day, but it hasn't happened since, and that was almost 20 years ago. Now, I feel pretty darn good when I do the occasional 5 or 6 pack.
A big key to large packages, is just happening to have a table that breaks real well at that time, and then finding the right spot and speed to break from. In other words, not having balls get tied up with each other. It doesn't happen very often.
edited: almost 20 years ago, not 30.