Why didn't anyone tell me this sooner? This rates almost as high as "it is not entirely your fault that you will be in a bad mood before your period" as things I should have been told sooner (like sometime during the 20th century).
I thought it was really bad genes and poor eating/ exercise habits that kept me from finding pants that fit. Well, maybe that's part of what's going on, but I love not being held responsible way too much to acknowledge this :) It's not my genes' fault, it's my jeans' fault!
So for starters, I'd bought a jacket that looked good on a fashion blogger I liked for about 8000 yen (never mind that said blogger is about 1 cm taller but 6 dress sizes smaller than I am). I knew the sleeves were way too long, so I spent a couple hours shortening them. Then, I decided the shoulders looked wrong, so I took my trusty 100 yen-shop seam ripper and took out a few stitches in the lining and removed the shoulder pads. Then I hand-stitched the hole in the lining closed. The jacket fits much more nicely around the shoulders now, to say nothing of the sleeves looking right post alteration.
In a delusion of grandeur, I bought a sewing machine. So far I have only used it to hem the Pumpkin Princess's new curtains, but when I get the hang of things, I would like to use it for DIY alterations. Because it's not my fault my clothes don't fit! And I need to justify spending the money on a new sewing machine (when I could have just winged it with my mom's machine)!