In none of these cases did the client ask for more time/energy and not get it; I gave more time and energy than would have been necessary with a properly run project. Just bad clients, bad contracts. They happen, and my point is that it would have been hopelessly irresponsible for me to invest all my hopes in just one or two.
To give you an idea of what I mean, the one that's in the process of falling apart took over six months of negotiation, periodic prodding, and concessions to get them to actually provide me fully signed documents so I could start work. The whole time they were telling me how excited they were about the project and how important it was to them. Clients like this all seem to exist somewhere on a spectrum, and you have to figure out whether they're just a 'less profitable' client because you'll have to put more work in (and set your hourly rate accordingly), or whether they're a fundamentally problematic client that will just never work out. This client turned out to be the latter, even if I am billing hours now.
I suspect once you've been freelancing long enough you can just say no to any client that seems like they could be a problem. For me, it's been a little over two years and the influx of work is not remotely enough to justify that (even if I get way more offers than I used to, and they're better offers)