There's only a slight satisfaction that comes from snapping your smartphone into its case. As designers we know that the case was injection-molded specifically for that phone, with a 0.005" tolerance and some draft angle; in other words, the damn thing is supposed to fit perfectly. Similarly, a diner will enjoy the concept of a turducken more than the chef who put in the elbow grease to cram all of those meats in there.
However, there's a huge amount of satisfaction that comes from slipping one object inside of a second, unrelated object and finding out they fit together perfectly by pure accident. It pushes our OCD buttons and our brain's pleasure centers light up on the MRI. I have no idea why this is, only that it is, and now there's a Tumblr I can't stop looking at called Things Fitting Perfectly Into Other Things.
Unsurprisingly, artist Michael Johansson, whose work we looked at here, is the unofficial king subject of this Tumblr.
At press time there were some 27 pages of submissions, so this oughta keep you busy for a while.