Have you experienced the pain of having a large database table with many columns to handle storing complex entities? Have you experienced the pain of having a large function or class so complex you won't touch it for fear of what will break?
It's common to try to use one model of of the elements of your domain to try to serve all functionality required. The truth, though, is that not all needs require the same model. Different parts of your problem look at the same elements in different ways. A customer is a credit card to your billing department and a mailing address to your shipping departement. They look at things differently and should use different models.
One of the main lessons of Domain-Driven Design is that a domain can be decomposed into bounded contexts where smaller pieces of the problem can be modeled and addressed. Learn about the ways you can use multiple models to build an model that is simpler and more useful.