Does "entity relationship diagram" help to build an excellent database structure?

If you are building normal systems, like few tables and data load is also not much then ERD is best solution..........but if you are developing complex systems with many many tables and handling data (DML) queries through your stored procedures then ERD doesn't matter.

the ERD like nigative of building, if engineer build the building without nigative this will cost him more and the building at the end will not be like customer looks too, so when you build the ERD you can modify it too many times as customers needs before start building the database.

I think nothing assist  you, in building excellent DB structure, more than Entity Relationship Diagram (ERD). Database Designing based upon a set of rules, principles and best practices but describing and verifying the final DB structure is so difficult without ERD.