I've unfortunately taken a car to its limits by neglecting to change the oil (depression). They go fine and then they fail quite fast and permanently. Amazing how long it lasted without any noticeable effects, though!

Most people change their oil way, way too often. Places like Jiffy Lube will tell you every 3 months or 3000 miles because they make more money that way, but if you look at your manual it's more likely to say 6k miles with crude and have no time based recommendation. Synthetic oil you can go something like 10k IIRC.