This morning, as I was annoyed as usual by the door between the dog lock1 not closing properly, I was struck by the inspiration to do something with it. I opened the door and looked at the hinges; it appeared that the upper hinge was loose. So I fetched a #1 Phillips screwdriver, and sure enough, the screws were loose; I tightened the hinge down. Now the door closed smoothly, but it didn't latch.2 Now determined not to be defeated by this pesky inanimate object, I examined the closing hardare and found that the strike plates for both the latch and the deadbolt were clearly too high.3 I proceeded to fetch the cordless drill/driver, drill bits in case I couldn't just screw the mounting screws in, a wood chisel and a hammer. Just a few minutes' work, and now the door closes smoothly without bumping into the frame, latches easily without being guided with a hand on the doorknob, and the deadbolt can be locked with just one hand on the key -- no more 50-lb pull on the doorknob with the other hand and hope the key doesn't snap because it's still tight.
1My house was originally built with a breezeway with sliding glass doors at either end between the garage and the house itself, with the front door of the house and the people door to the garage opening onto the breezeway. A few years ago, I had the breezeway remodelled into two small rooms, with actual walls and doors on the ends instead of the sliding glass doors. The back half has a dog door opening onto the fenced backyard and serves as the dogs' shelter from inclement weather when I'm not home; the front half has a real front door for the house and serves as a mud room, non-climate-controlled storage, and most importantly, an "air lock" ensuring that there are two normally-closed doors between the areas where the dogs are supposed to be and the unfenced outdoors.
2This triggers some dim memories of one of my neighbors helpfully "fixing" the door, which wasn't latching securely. Post-"fix", in some weather the door actually worked OK, but most of the time it's been tight against the door frame and the deadbolt is hard to operate.
3This seems counter-intuitive; tightening the top hinge should make the door ride higher. But I'm not going to argue with or try to analyze the reality on the ground (or in the wall in this case), that with the hinge screws tightened, the tongues of both deadbolt and latch were hitting the metal on the bottoms of their respective strike plates instead of fitting into the holes.