Contemplation

Sunset in my neighborhood August 2018

“The best predictor of future performance is past performance.” That was accepted logic in learning theory when I was in graduate school in the 70s. 

It is the fundamental assumption of regression and general linear models that statisticians have used for the last 100 years. Whether performance is linear or curvilinear, it is predictable. The relationship holds true for people, widgets, or systems. When it seems to fail, it is only because there are insufficient data.

People buy stocks based on their past performance (return on investment over a 1, 5, or 10 year period), despite the warning in every prospectus that past performance is not a good indicator of future performance. Why? Because the controlling factors are themselves in a constant state of change. That change, once recognized, leads to predictable outcomes, however.

A few weeks ago, I was discussing with a surgeon the most likely response to alternative treatments. I was using the consistency of past experience to predict a future positive outcome. He was counseling a conservative approach. He said, “You would hate to be right, until you weren’t.” I think that is a direct quote, but if it isn’t, it certainly captures his intent. The sentence made an immediate and lasting impression on me. In context, I understood him to be saying that my past experience might not be as relevant as I thought it was and so I might be wrong in using it to predict the outcome. He was saying that responses to similar treatments can be consistent, but that they can also suddenly and catastrophically change with a new treatment, even if it is similar.

As someone who understands generalization gradients in the specific case, as well as the broader human tendency towards logic errors as a result of overgeneralization from the familiar, I realize that I am guilty of expecting life to be linear and predictable, not capricious nor chaotic. I expect change to be gradual, not abrupt. I wonder if stress is caused by the belief that life has become unpredictable and that there may not be a return to normal or a regression to the mean.

I smile when I think about a colleague from the 90s who had a card sitting on her bookcase. It read, “Change is good; you go first.” Another example of a brief moment in time, that changed my way of thinking for years to come.

I am coming to understand that change is the hallmark of growing older. Managing it when we can and managing our response to it when we can’t, is the primary work of elders. It makes me think of the serenity prayer.