The author asserted that the probability of the event in question was approximately

(1 - 10^-21)¹⁰²⁵

How small is this number?

So far others have tried the 1/e solution, but how about this one.

10 to the -21st power is a very tiny number (a 1 with 20 zeros in front of it).. 1 - a very tiny number is very close to 1, but less then 1.

(.999999999999999999999)^(1^26)

1^(1^26) would still be one, but just a little less then 1 would cause the number to decrease, so the end result is something like

(.999999999999999999999)^(1^26)=

  0.999999996003097

Seems like a pretty sure thing.