“For the fragile, the cumulative effect of small shocks is smaller than the single effect of an equivalent single large shock.”

“For the antifragile, shocks bring more benefits (or less harm) as their intensity increases, up to a point.” Ex: lifting a 100lb weight once is more beneficial than lifting a 1lb weight 100 times.

Your flight never gets in 4 hours early, but you can certainly arrive 4 hours late. Anything unexpected, any shocks, is much more likely to extend the total flying time, ergo flight schedules are fragile.

Another example: Don’t cross a river if it is “on average 4 feet deep.”