5,000 is a good milage interval. 3000 is a myth & unnecessary. If you go much over 5K, at least change the oil filter, and I wouldn't go much over unless using synthetic.
Yeah, if you go 12K, you might not notice any problems, the engine just might not last as many miles. Just because some people go extreme milages and either get lucky or don't notice long term damage, doesn' t mean it's OK or advisable.
When I worked in the car business, I remember seeing several cars w/ oil related damage. Like a current year model car w/ 25K which never had an oil change, and thus had locked up engine. A sludgy mess. Pull the plug and it runs out very very slowly.