Aircraft don't look like it, but they are precision-assembled vehicles.
The wings on an aircraft get trued up using a theodolite good to something
like two arc-seconds: 1/648,000 of a circle, 1/1800 of a degree. The wings
on an F-105 are (or were) allowed to be out of true by something like 5
arc-seconds: 1/720 of a degree.
Truing up a pair of wings keeps the pilot from having to crank in left or right aileron trim, which pilots find irritating: the aircraft really should fly straight and level on its own.
Lots of things should happen. Not all of them do. And one of our F-105s, no matter how carefully the airframe guys trued up the wings, wanted to go corkscrewing through the sky in a slow roll to the left. It irritated the pilots because they had to crank the trim control almost to the end of its travel. It irritated the airframe shop because it was a problem that they couldn't locate and fix. It iritated the techreps, because it meant that there was something wrong with the way one or the other of the wings had been built, or with the way the fuselage had been built.
That F-105 was still wanting to roll slowly to the left when every F-105 was taken out of the active fleet and replaced by something a good deal more modern, and nobody ever found out why.
Postscript: I can see that aircraft, now in the fleet of some third-world country, still trying to do a slow aileron roll to the left, the crew chief and pilot raising Cain with the airframe shop, and nothing they do having a bit of effect.