Irrationality game:

There are other 'technological civilizations' (in the sense of intelligent living things that have learned to manipulate matter in a complicated way) in the observable universe: 99%

There are other 'technological civilizations' in our own galaxy: 75% with most of the probability mass in regimes where there are somewhere between dozens and thousands.

Conditional on these existing: Despite some being very old, they are limited by the hostile nature of the universe and the realities of practical manipulation of matter and energy to never controlling much matter outside the surfaces of life-bearing worlds, and either never leave their solar systems of origin with anything self-replicating or their replicators on average produce less than 1 seed to continue. 95%

Humanity has already received and recorded a radio signal from another thing-analogous-to-a-technological-civilization. This was either unnoticed or not unequivocally recognized as such due to some combination of very short duration, being a one-off event that was never repeated, being modulated in a way that the receiver was not looking for, or being indistinguishable from terrestrial radio noise. 20%.

Conditional on the above, the "Wow!" signal was such a signal. 20%.