A couple of years ago, before I re-started serious weight training, I stuck a bar for chin-ups in my house. It's a bit of 50mm square steel tube, and I've put it across a hallway that I often pass through, about 220cm up, so that I can grab it if I reach up a bit.
I'd pull myself up whenever I walked past and remembered it.
Not very long after, and without having put much thought into it, I noticed one day that my lats were obviously much improved (in contrast to the rest of my neglected, middle-aged body).
This motivated me to get back into it ...