Ok, I'll give an example.
I need a new bed, I went through the process for a few months of debating spring or foam, and platform or daybed and finally I've decided that I will build it because it will be cheaper to do out of 2x4 wood than to buy a frame and mattress. I have the frame spec'd out in sketchup, my SO did it because I was stuck, my computer is old and crappy and so is my internet connection and the program is no longer downloadable so I either need to finally purchase a new computer (which is something in the works, I'm looking for a portable 3.5 pound or less laptop that runs linux. I just haven't found one in my budget yet, and if I get used I have to deal with all the things that come with that, and replacement parts might costs as much as a budget laptop. I also need to figure out what's wrong the internet and possibly buy a new router. It took me weeks to find the manual for the stupid thing so I can start playing with the settings when I have energy. The account is under someone else's name so I can't troubleshoot it directly with the company because I don't have access) or to find the old program. So I basically was already stuck till he bailed me out. Now I'm stuck again because of the drill.
Neither of us have build furniture or done anything with wood, so I don't know if it will hold up, and how to approach doing a test build to see if it's going to be a waste of money (which is tight for me, so I can't really afford to waste money and I need to go cheap). I will need to purchase tools to build it (drill). I've figured out that home depot will cut the wood for us so I don't need a table saw (which isn't going to work in my studio apt), and I hear they don't do the best job, but it's probably better than what I could do. My SO has a hacksaw so I guess we can fix it if there's a problem.
My goal is to spend as little as possible on the bed but still have it be comfortable. I've been wanting a drill for a while, and right now the price of the drill is out of budget, so I either have to wait for the price to come down or borrow one from the tool library. The drill I've chosen is reliable, but not corded. Corded drills are cheaper, but the only one I can find is a black and decker and people say those are shitty and break, and I'm not wasting money on a throw away tool. I'd rather have a drill that will last and that I can sell if I wind up not using it. If I borrow one from the tool library I need to leave collateral (something I will return for, like a driver's license) and I don't want to leave anything with private info or important to someone I don't know. I'm building the bed in three sections with storage so I can basically turn it into seating when people come over (lieu of a daybed).
I will also need to buy foam and have it cut to size and I don't know where to buy it or if it will make me ill, as I've been ok with some foam mattresses, but not others. I could alternatively buy a mattress but I've tried a bunch in a department store and mattress chain and found them to be too expensive and/or uncomfortable. If I buy an affordable one from a mom and pop discount store I won't be able to return it. If I order online I could decide I don't want it, but that's a waste because they get tossed. And I might have to deal with foam off gassing and don't have a place to put the mattress to air out since I live in a studio (which is why the bed needs to convert to seating).
I think the buts and unknowns tend to get in the way. I don't know how to schedule all of this. So maybe I kinda know how to break it down, just not how long it will take and if something holds it up, how that works. I tend to freeze when there are choices and just let the project die.
I've looked at Tim Ferriss's Fear Setting technique (he has a layout). I still have trouble with when there are unknowns, like it's totally new and I don't know what I'm doing, or have choices down the road.
This thing is taking me so long that I've considered just buying a new mattress and sleeping on the floor, since my current mattress (on the floor) is in such bad shape I can't sleep well anymore. Again I get stuck with spending $400 plus on a mattress, it's quite a lot of money for something that might not work out. I've spend money twice on mattresses I hated and fortunately moved 6 months later (for both) so I was able to get rid of them (I wasn't able to sell them, one I gave to a friend in exchange for storing my stuff and helping me move, the other I gave to family). I'm not really in the place right now to throw away $400 which is why I've waited so long in the first place. I'm mostly worried that I'm not doing enough research on how to build the bed correctly, but I'm getting to the point where I want to just build at least a section and see how it turns out. I kinda want to get this over with. I guess I can always use it for something else if it doesn't work out. I should probably buy the foam cushions, sleep on the floor and test out the bed frame in pieces till I get it right.