A system / product (software, website, …) must be
- Relevant : Your problem can be solved by this system. It fits into the big picture, it answers a need
- Reliable: You can trust the system to help you and deliver on your expectations, provide accurate information
- Reachable: You can easily reach and the system and / or the functionalities you need in it
By assessing your current systems against these criteria you can judge how well a system is accepted by users.
This is what I call UX outside the product. You can have all the magic UI tricks in the world inside your product, if it’s not relevant, reliable or reachable: it’s going nowhere.