Imagine you have a bunch of crappy and unrealistic theories about why something occured.

What those phrases mean is that the lab leak is simply the least crappy theory.

Imagine if it's a curve like this:

- No idea for either solution and we'll never know - 70% chance

- Lab leak - 20% chance

- Occurred in nature - 10% chance

In that case, you could say that the most likely answer is "lab leak" if you must have an answer, but it's very "low confidence." I don't know what the actual odds are, it's just made up for demonstration.

“We don’t know” is by definition not a theory though, it’s a lack of a theory.

"we don't have a clue" is not a theory about the origin. It's a theory about your knowledge of the origin. It's not in the pool of competing theories you're considering in this context.

True, in this case “nature” is basically the catch all “not lab” theory already including the probabilities the source is "not lab but we haven't named the source".

Check out the video I linked above about Survival Heuristics and Avoding Intelligence Traps.

Its fairly standard SOP. If you don't know what it means that video explains it fairly well.

Well say you have one theory you reckon has 40% chance of being correct, one theory with a 5% chance, and one theory with a 55% chance. One theory is more likely than any other, but is still almost as likely to be incorrect as not.

Plus "none of the above" is always an option. You could have 3 theories that all have very little supporting evidence - one of those theories could be the most likely of all the actual theories, but "none of the above" could be just as likely if the best theory is still weak.