Why can't pants be welded?

Today I decided to take a moment to alter my jeans. Big mistake! Although my jeans need alteration in order to be comfortable, I hardly think it's worth actually sewing them. I have a large enough butt to fit them, but the waist is too loose and it bugs. So at the advice of my aunt, who tells me wearing a belt just adds bulk, I decided to sew little darts into the waist. (Dart: A tapered tuck sewn to adjust the fit of a garment. I looked it up.)
Now, this may sound like a simple operation to you, but remember that I am the girl who, after a miserable semester in Home Ec, transferred to metal shop. There is a reason I learned to weld: Sewing machines hate me. Replacing a button with needle and thread, no problem. But a sewing machine??? OK, there was that one quilt I made, but it was straight lines only and I must have had some divine intervention. Since then, every attempt at sewing for me has been filled with thread clumps on the underside of the material, and large clumps of hair being removed from my head.
Today was no different. The machine was already out and threaded from a previous alteration fiasco, so I sat down and tried my hand at two simple darts. The upper thread was almost gone, but hey, how much thread does it take for two small darts? I neglected to take into account the large scribbles of thread that hide on the underside. They use a LOT of thread! So there I was, one dart done without much screaming, working on the second dart. Suddenly the machine makes a sick THUNK noise, the empty spool of thread goes careening across the table, it's spool-holding rod now unattached and clinking onto the table, and my needle completely stops mid fabric with the needle tip stuck. It was the closest I've ever been to anything like a sewing machine explosion. Frightening really.
After retrieving the spool and screwing in the rod that held it, (I really don't know how that came off!), I realized that I had actually BROKEN the needle. The thick METAL needle. I broke it.
I do have some consolation. I only have to wear my jeans lopsided for a small amount of time until I can take them to my Mom for proper alteration. One of the benefits of having a talented Mom close-by is that I can run to her after I've half-ruined something and say "Can you fix this?" And for sewing things, she usually can. She has a secret weapon. She has a SERGER! That's right--buttons, bells and whistles, multiple spools of thread, internal computer SERGER! If she knows what's good for her and her machinery, she won't let me near it.