This is a meme that gets repeated often, always with no source. I bet you heard this from someone repeating it exactly in this same context too, complaining about security theater.

Not everything in life (in fact, almost nothing) can be “proved” by a “source”. Human emergent behavior can be observed and reported on in this way, perhaps.

But questions like “why aren’t more people sacrificing their lives to hijack or destroy airplanes for the last 20 years” are not answerable by “sources”.

Do you have some reason to think a different posture towards hijackers and better security around cockpits didn’t have a strong effect on would-be hijackers’ willingness to give their lives to a violent political statement?

Nope, but I can’t prove my source (despite it being a reliable one), so I’ll retract. Continue on with your life thinking everything is a meme!