In Katamari Damacy, advancing to the next size threshold makes smaller objects disappear and enclosed areas inaccessible. In some cases, you start out inside a building that you can later roll up.
Part of the challenge of trying to collect the entire catalog of objects is knowing when you can reach something and when it’s too late. But, of course, you might as well not even try to collect all of the objects if you’re playing a game that includes Cowbear.