Data modeling is so critical that you will want to spend a good chunk of your time on that. Most of the features in your application are built on top of the data models that you created. If your data model design has flaws, you will need to introduce weird logic to cover corner cases that are not included in the data models. And, in the worst case, as the application evolves, the terms in the code no longer match their meanings in the data models.

A good data model design is a result of a deep understanding of the requirements, solid knowledge of the database, and the practicing of domain-driven design.