Ambition is a big part of it for me. If I set out to make a grand megaproject I'll lose interest quickly and never return to that fort, let alone that world. But if I set out to simply build a powerful fortress with virtually no plan, it may survive for decades.
If you suffer from procrastination in everyday life, don't set out with a plan or you'll procrastinate yourself right back out on the streets, starting a new fortress.
If it's OCD that's killing it, tell yourself that the design you're going for this time around is complete and utter chaos regulated only by necessity. Your OCD will still control how it turns out, but it can help prevent you from trying to savescum or quit altogether for every little thing. You will achieve perfect chaos, which will help in the next part:
The hardest thing to accomplish is defeating sheer boredom. Try embarking on more complex and interesting landscapes like high plateaus around river junctions that may or may not involve waterfalls, or search the world for volcanoes that only register as one square on the relative elevation map (the one displaying basic blocks from white to dark blue.) and build forts into their walls, especially if there's a deep river canyon on that embark. After that, don't go the efficient route or try to set up a military or serious industry; the more !!FUN!! you have, the more fun you'll have. Be overconfident with your enemies and try to defeat them with pure dwarfpower. Don't cower from FB's, although a little caution is advisable. Soon You'll be laughing your ass off while trying to get your fort back in order.
I actually have a link to my mod in my signature that tends to make things infinitely more entertaining military-wise. Both the EVIL mod and the dragonkin pack will provide some difficulty and possible entertainment value. I intend to update it soon. Really...