What are the main criteria for a multi-user application?

Question

Programming

I create a multi-user application, the usual accounting of products.
Interested in the question of how to make such applications correctly, what is important and what is not?
What are the main criteria for such programs or the correct logic?

Answer 1

1. Reliability and fault tolerance (separation of access rights, backups, conflict resolution, etc. etc.)
2. Implementation cost in relation to functionality
3. Performance (including maximum response time, network load, etc.)
4. Convenience of the interface (both administrative and user)

Answer 2

Performance is the most important