Why is it always the last place you look when you find something that was misplaced?

Because when you find it you stop looking.  Always be sure to remember where you left off so you can start looking there the next time you misplace something (I mean, if it was there once, it might be there again).

Because you get desperate and you start looking in the least place you'd ever expect to find the lost item.

Just assume you have looked for the misplaced item in all the first places you'd search then go straight to the last place to look and then find it.

It's one of those laws.  :)