So I am curious- Mod/Upgrade Fails?

This is one of the best threads I've read in a long time.  Great idea!  
A little story here and a little advice:
In 2006 I got an opportunity to work for a guy that wanted to start building custom cars. His name is Neil.  I quit my work as a remodeling carpenter and we went at it full time. I worked with him until in 2016 when some physical issues forced me to retire for good. We did some amazing collaborative things and had some amazing success that took both of us by surprise.  Many of the projects we got into he purchased as uncompleted basket cases from previous owners who had spent thousands of dollars on, then abandoned, mostly because the owners had gotten in way over their heads, lost their way and couldn't bear to see the mess they had.
We quickly developed a mantra that the last 10% of the job took 90% of the work. It's a maddening, frustrating thing to have a project so close to "finished" but still looks like a homemade haybine. Neil was running 2 businesses full time, but I worked in one of his shops so we chatted often throughout the day. We talked about direction often and I still believe that the key to our success is a term I stole from a book I read about how our eyes work. That term I stole is called: "persistence of vision".  What that meant to me is how I would "visualize" each single step in a project. No matter how complex a project, or how long it took to do, I would actually go through the whole thing in my head before starting, like a race car driver visualizing each turn in a race track. Then, and this is the most important part, I would work methodically, avoiding any urge to sit back and look at the whole thing, and just tightly focus on the immediate steps over the next few hours or days. If you have a good plan and can see the steps necessary to complete it, you'll get there. Avoid looking at the whole project because it will appear overwhelming. Stay focused on your steps and you won't waste time bouncing from end to end, putzing with something that doesn't need your attention right now. It's tempting to want to go and clean up a wire run or "just hook it up quick" to see how it's working. Avoid that and focus on what's in front of you.  Stay true to what you have "visualized" and you'll get there. You can (nearly) always go back and tidy things up during that last 10% of the job. Problems will always arise, but just take the beatings one at a time and don't move on until you are satisfied with what you have done. That works for any job, big or tiny. Be true to what your mind's eye can see. You'll be surprised at how accurate it is....

And, VictoriaP,
Don't kid yourself or let anyone lie to you:
NOBODY can drill a centered hole in a bolt....
WilliamA