When is change in a relationship a good thing? When is it a bad thing?

I guess it depends on the person and the type of relationship. For example if you have a boyfriend or a girlfriend and you guys aren't serious and then you get serious it could be good or bad, it all depends on the person and what you think about about relationships, for me if this happened I would think it was a good thing, because I don't think I would even like to have to non-serious relationship. If there was a change like we were serious, but then my boyfriend started goofing off I would think that is a bad change.