In wedding planning and house renovating, there are approximately one bajillion details and decisions you can pursue. For most people, though, there aren't one bajillion dollars to bankroll said options, so every step of the way you're reassessing the budget and what's feasible.
2) Everything costs more than you think
I have never run into this issue as noticeably as I did when wedding planning and when house renovating. Going along with point #1, you want to make sure you get the most bang for your buck and stretch your dollar as far as it will take you. It's continually frustrating when you come up with a price point in your head for a purchase only to discover you underestimated by about 25%. And don't even get me started on the headache that is tax and shipping at the end of an online purchase.
3) Treadmill to-do lists
Whenever you're trying to get everything finished and as close to perfect as possible, it's nearly impossible to turn your brain off from the constantly evolving to-do lists. I can't tell you how many times I would need to reach for the nearest scrap of paper, hoping to jot down the two or three tasks I had just remembered before the vanished from my brain again. You work as hard as you feasibly can, and it feels like you get exactly nowhere in relation to your finish line.
4) Aiming for cohesion
No one wants to go to a wedding that looks like four different people orchestrated it, aesthetically. In the same vein, no one wants to walk into a house that looks like a group of strangers banded together for an ill-fated design project. Colors, themes, feels, textures, looks, whatever you want to call it, during the labor phase, you have to circle back with yourself and make sure you're still on a path to somewhere and not producing something that smacks of insanity.
5) "What have I gotten myself into?"
Whether it's a disagreement with your spouse/partner/betrothed, a "simple" problem that transforms into a catastrophe, or just the general fatigue this process forces upon you, there is definitely a point in time (or multiple points in time) when you secretly wish you could undo the whole thing and go back to the way life used to be, regardless of how stunted your personal development may be as a result. And those moments suck.
That said, there is one big, fat, honking difference between fixing up a house and planning a wedding. And it hit me like a ton of bricks.