” What is? is. What was? will be. What will be *was*, but will be again.”

Quoted from an episode of the TV show “Welcome back Kotter”

The basic logic of this quote is that events occur in cycles.  The only thing you can be sure of is the current cycle, (what is) but predictably the past will be back.

Past Behaviour Predicts Future Behaviour

Analysing past behaviour to determine the future is not an absolute and investment advisors ( to pick an example of a profession frequently trying to predict) regularly provide caution about using this approach to determine which funds or equities to purchase.

They advise, there is a real risk upcoming events will be unique and not influenced by historical at all.  For example, the government might introduce a new tax or policy that impacts behaviour.

Balanced Predictions

Past behaviour has been a proven predictor of future behavior in a number of psychology studies I have read.  That being said, the unexpected does occur and can significantly impact a future event.

Given  both these factors can have an influence on future predictions,  it is the balance you draw between behavioural predictability and the unexpected that will drive the accuracy of your predictions.

The future predictions you make will have a risk of inaccuracy, but careful consideration of past behaviour, event cycles and possible unexpected occurances should enable you to have some confidence in your forecast.

This is a bit contextual as some things are clearly more volitile than others, and so harder to predict.

Most pragmatically, what is: is ; what was: was and what will be: will be.  As the pseudo Spanish lyrics say, que sera sera (whatever will be, will be).  The future is not ours to see.