I'd say that I usually bat pretty high on fixing problems on my railroad. I'm a compulsive tinkerer so I tend to fix broken things even if it takes multiple efforts for success.
Here's how I usually categorize projects:
Easy fixes (50%): Turns out it just needs routine maintenance, a reattached wire, some fresh grease or something similarly easy to get it back running again. These usually stay fixed as long as I maintain them and of course, stop messing with it once it's back in order.
Skilled fixes (25%): These fixes make me feel smart. Sometimes I'll buy a fixer-upper locomotive because I recognize the problem it has from the description and with a little work and a cheap part, I now have a great engine for a bargain price. Awesome!
Pain in the Butt (25%): These fixes make me feel stupid. After pouring in hours of work, the problem really isn't fixed. Usually I can sorta kludge it together but if it isn't fixed right (or the problem keeps coming back) then I'm not happy. Aaaargh!
Come to think of it, this applies to my day job as an electronics test engineer too!