Both plots were not only viable, they were successful.

Richard Reid may have thought he was going to blow up an airplane, but whoever set him up didn't expect him to. The same with the liquid bombers. If an airplane disappears over the ocean it can take years to figure out exactly why, if at all, which isn't terribly useful for terrorists. If some inept bomber gets caught doing something with a shoe, a small bottle of liquid, or something in his underwear, no matter how unlikely the chances of destroying a plane, the countries under "attack" inflict damage on themselves in the form of things like liquid bans and shoe removal, restrictions on freedoms, and increased use of resources to implement the bans/searches for fictional dangers. Some cheap shoes with a fuse sticking out have cost the US many billions of dollars.

It's essentially terrorism theater designed to set off our security theater, and it's been very successful.

I used to bring at least one 2 L bottle of seltzer on any transcon flight, and now I'm limited to a few cups, or maybe a few cans that the FAs hand out. And I have yet to see a US airport that sells seltzer airside - it's still water only. I want my seltzer back.