Dr. Sacks continues writing about a patient he calls Mr. MacGregor.

Mr. MacGregor lives in Parkinson’s disease. He walks with a tilt. And, he was unaware of that tilt until he met Dr. Sacks.

Upon learning of his tilt walk, MacGregor did what any person would do — he stopped and tried to figure out the problem. He ended up learning that there’s an internal “spirit level” in his head that he can’t use — a level is used to align things. To combat his inability to use his inner level, he created glasses which had a level (of sorts) attached.

The glasses, while bulky, allowed MacGregor to walk upright and orientate himself.

I marvel at how beautiful MacGregor embraced the constraint.

“‘So that’s it, is it?’ Asked Mr. MacGregor. ‘I can’t use the spirit level inside my head. I can’t use my ears, but I can use my eyes.’ Quizzically, experimentally, he titled his head to one side: ‘Things look the same now — the world doesn’t tilt.”

However, the mirror would prove impractical. Who walks around surrounded by mirrors?

“I’ve got it! I don’t need a mirror - I just need a level. I can’t use the spirit levels inside my head, but why couldn’t I use levels outside my head — levels I could see, I could use with my eyes?

… Then, with the help of our optometrist and workshop, we made a clip extending two nose-lengths forward from the bridge of the spectacles, with a miniature horizontal level fixed to each side… In a couple of weeks we had a complete prototype… This worked.” - Oliver Sacks, “The Man Who Mistook His Wife for A Hat” [abridged for clarity and brevity]

Apparently the glasses were the talk of the town.

Embrace your constraints.