UML lets you try to do too much and make it too complicated.
One of the creators of UML has said that it’s “dead”. It got too complicated. The UML 2.0 Spec is >1000 pages long.
Know why you’re using UML. Is your Modeling Purposes to create something simulatable? You probably shouldn’t. Instead make something that’s incomplete, but more clear. Effective communication is more important that exhaustive completion.