So I agree, some ideas are more manageable than others. But the only thing I'm getting out of your description is that a co-founder validates ideas, because you don't trust yourself to know that Hyperloop is harder than a Reddit clone?
Also not sure if you could be fooled into thinking Hyperloop was easy, why you wouldn't be able to find an equally optimistic co-founder.
Your last sentence gets at the heart of my point. If you wanted me to come on board with your idea that builds on hyperloop, I wouldn't be "agreeing that that's a pretty cool idea and should be on your list." I'd be agreeing to actually build it somehow.
So the standard for cofounding something is a million times higher than the standard for putting it into some list of ideas.
Also not sure if you could be fooled into thinking Hyperloop was easy, why you wouldn't be able to find an equally optimistic co-founder.