According to the user-centered design philosophy, the end user of the product is the king. While designing the product (the product could also be a service, website etc.) you need to always meet the needs and wants of the end user. This also means that you have to test your assumptions through prototypes to make sure that the user needs are met.
Using simplicity will definitely not make the design process easier, but it almost automatically covers the user-centered design philosophy. When you use simplicity while designing your product you will need to see the product from the user’s perspective to really understand what is needed and what is not. You will need to go through iterations of removing and adding things, until you are left with the essential and useful.
After all the iterations and prototyping, if done correctly, you will start feeling like you’ve embodied the end-user’s wants and needs. This will allow you to create a product that is easy to use and feels familiar, even if it’s a new invention. We want to get to a point that we have covered the user’s wants and needs, and do it in a way that doesn’t seem that foreign to the user.
In the end you will have a product that will be easy to use and feel like it was created to cover their needs.