I want to thank everyone for their insights and stories.

I found the psychological explaination helpful, because I had made the
connection between the event and my first pair of bifocals...which indeed
forced me to doubt what my eyes were telling me.  I still have to take a
second look when something appears to be plumb...or out of plumb.  But it was
also a time of doubting my instincts and impulses.  I suppose this means that
it may or may not happen again, but we won't know until it does or does not.
Obviously training would help.

So I want to thank all of the suggestions in terms of training too.  The
description of the difference between cavers and rock climbers was
thoughtful.  That might be a good way to go.

Monday morning.  Let's get out there and make some history.

-jc