[smt88]

It's probably better to think of bubbles as the accumulation of unsustainable behavior.

Obviously we aren't able to predict a few months into the future, let alone a hundred years, so it's hard to definitively say whether current behavior is sustainable for a hundred years or not.

It's much more reasonable/believable to say that current behavior is unsustainable for 1, 5, or 10 years.