I live in a 1911 house built for a family that had a cook and a housemaid who were short, coming from undernourished countries like Ireland and Sweden, so the back stairway has low clearances, where Mary Margaret or Inga used to hustle down to fix breakfast, and where I now clomp down for coffee eight or 10 times a day. There is a low overhang a few steps down from the second-floor landing, where I have banged my head several hundred times and today when I banged it again. I heard chortling from a small person behind me and could not express my indignation as fully as I might.

I have lost some vocabulary bumping my head on that plaster but not the words that come to mind when you get a good crack on the head, but here is my child laughing and saying, "Do it again." One man's misfortune is a little girl's amusement.

A good hard bump is a moment of truth which announces that (1) the world does not conform itself to our impressions of it, and (2) even if you duck and weave your way through the jungle of life, there is an overhang with your name on it, and (3) it is good, at a time of Gay & Lesbian Literature and Women's Literature and red states and blue and persons of color and non-color, to get a simple universal experience that is available to everybody (BONK! Arghhh!), and (4) I forget what the fourth point is. Something about suffering.

This particular bump was a hard one and I sat down for a few minutes, not to feel sorry for myself but to get the full benefit of the experience. I could feel some revelation forming itself. I once slipped while running on a slippery dock and instead of landing on the edge of the wood slats and breaking my spine and starting a new life as a paraplegic, I landed fully in the water (which covers three-quarters of the world so statistically your chances are good even if they aren't really) and out of this came some revelation of God's grace and mercy. Not that it changed my life — it didn't — but it was memorable.

This particular bump made me think of my old journalism teacher at the University of Minnesota, Robert Lindsay, a gruff man with a big shiny head with a deep dent in it. The dent looked like a direct hit by a mortar shell. Professor Lindsay had fought in World War II and the Korean War as a U.S. Marine, retiring with the rank of captain, and now he was teaching a writing course to sophomores five days a week, a fresh assignment every day.

Though we were in journalism, none of us spoke up in class and asked Mr. Lindsay how he got that dent in his head. We were scared of him. He had a rule that any writing assignment that contained a misspelling would be an automatic F, which struck us as horribly unfair. What if you wrote something utterly brilliant but had misspelled one little teeny-tiny word? "If you're not sure, look it up," he said. "Learn what to be sure of and what not to be."

We think we want teachers for our children who will nurture and encourage them (You Are All Special, Each In Your Own Way, So Be Yourself And Follow Your Dream), but Mr. Lindsay was a teacher who gave good value. I was not a proofreader when I enrolled in his course and when I got out, I was. I still am. Simple as that. And he brought an ex-Marine's eye to lit'ry pretensions that had served me well in high school and he triple-underlined them and wrote "What's this about?" in the margin. And sometimes "B.S." And once he wrote, "Oh for God's sake."

I saw Mr. Lindsay a few years before he died, and he was warm and friendly and proud of his old student, but I was still uneasy around him. He had become a permanent useful growling presence in the back of my mind, saying, "You can do better. Go back and check your work." And I would, sir, but this column is due now, but I will strive to do better in the future, sir. And thank you, sir. Whenever I hit my head hard, I will think of you.

Garrison Keillor's "A Prairie Home Companion" airs from 6 to 8 p.m., on Saturdays on KHPR FM 88.1 and on Sundays on KIPO FM 89.3 His column appears Wednesday at www.honoluluadvertiser.com/opinion and in Sunday's Focus section.