We’ve all done it. The MOC is so close to being finished, but then you spot a huge, obvious mistake you made that means you have to take apart whole sections just to fix it. Here, you may share your embarrassment for all to read…
Here’s mine:
Just finishing up a MOC with a really complex torso, it looked great. Then when I looked again, I had forgotten to add a ball joint, where the head was going to go. The whole torso had to be dismantled, but then I forgot how it was built… 
I forgot to add ball-joints for the arms on one of my MOCs.
Well, with my Self Moc WIP.
Initially I thought I was, for the most part, finished with the legs, so I tried to continue with the rest of him, until I realised…
They were too thick. The half-arch technic pieces on the lower legs have been throwing off the rest of (if any) the Moc. I am still unsure as how to replace them without majorly changing the lower leg design, which I’ve really liked.
Switching between grey and black three long axles (as well as red and black 2 longs) throughout the MOC and your OCD eventually gets a hold of you and you’re forced to take apart the whole MOC to use only one colour of axles.
I find that fairly easy if it’s just a case of “push this one through while simultaneously pushing the old one out”
Not for a really complex build where the space to push the old one out is filled in with other interlocking connectors 
Yeah, that’s when it sux…
when Im just going to finish my moc, and I find out that the limbs don’t fit/have a low amount of articulation/are ugly
Back when I first transitioned into using custom bodies. I used to have this problem where my designs would often wiggle at the hips. I’d fix them later, but it was a very strange habit to have for a while.
Finding that third black axle to prevents any complaints from red and blue axle pins 
Finding a good design you like then when you finish you realize that becuase of the build that design ruins the look (having a gut, can’t stand, etc) and you have to redo it.
Also that one peice (cloths mostly) you need so you order it and the bodies already complete. You get the peice than have to redesign the body becuase that peice has all the connections you didn’t account for or know of.
making an leg that’s freaking awesome, then realizing that you don’t have the parts for a symmetrical build 
I’ve done that once or twice, so now I tend to make them both at the same time.
same, that one time changed me forever
*dramatic music *
Never fails.
I think “I need 2 of a piece. Piece , piece B, or piece C will work. I’ll just use whichever I find 2 of first.”
I find one of each.
If I need four, I find three of each.
Every.single.time.
Also, there was one time I needed a small technic connector. I reached into my big tub of black parts, grabbed a random piece, and pulled out the exact piece I needed. I just stared at it for a moment thinking “how did I do that?”
MOCING ISSUES ARE NOT SOMETHING TO LAUGH ABOUT…
I had a lot of problems making my self MOC.
Like, I had this amazing wing design… But didn’t have enough parts for a pair of them.
But
seriously thought
you know how there’s always that one useless piece you keep seeing laying around everywhere
then the moment you need it you can’t find it
ugh i hate when this happens
Mine would be the original design used for my self moc’s thighs. I was using bohrok torsos, but the way I connected the pieces caused a problem with the knees. I had a technic beam at an X orientation to build around.
Currently I have an issue with the ccbs frame being used in my self moc. It’s the one used in 2015 Onua. It obstructs full movement of the arms and sticks out too far with the ball sockets. I can fix this easily, but requires me to cut the piece, so I have to wait until I can get a gift card to use on bricklink.
Do you ever just see a useless piece so much that you put it in another place so that you don’t have to see it again…