There's nothing absurd about “you know when you see it”. Those are just things we don't have (or can't have, or don't yet have) good definitions for, but do exist.
"Family resemblance" [1] classes of things are often like that.
"What is a game", is a classical example. Any definition you can give can be violated, including "having a goal", or "not having real impact" etc. And yet we know a game when we see one. And there's lots of other such distinctions.
With “consciousness” in particular having good definition became important since there are a lot of discussions about “is AI conscious?” which might in the future dictate policy decisions.
If it weren't for consciousness your body would not survive, or grow to adult size, or reproduce. Of course, 'get something to eat' sounds simpler than it is in reality - you would need to be able to see, walk, grasp, understand the environment and objects at your disposal, shop, cook, earn money, be a functioning member of society - the whole bag.
In my view, life is a process that is governed on the grand scale by evolution (species adapting to the environment) and on individual scale by consciousness (individuals adaptating to environment).
Bacteria do both, like humans. Some AI agents also do both - evolution and learning, such as AlphaGo, just that its environment is a Go board.