After locking my door and getting in my car, I always feel like I didn't lock it and have to get out and check it. I have yet to discover I did forget to lock it, but it doesn't stop me from checking.
My mom has 5 cats; she has always had multiple cats. Anytime I go to her house I have to walk around and make sure I see them all.
My partner messed up his arm in an accident and it's been kind of a constant pain for him lately, even though he doesn't complain about it much. Anytime I wake up in the middle of the night I roll over to make sure he isn't laying on his hurt arm.
I have my dog in the car with me a lot. I would say I ask my partner "What's Norma doing?" at least every five minutes when she's with us; absolutely paranoid she will... I dunno. Open the door? Honestly don't know what my freak-out there is about.
When you leave give the door knob a few good twists and a push. ---