User experience, or UX, is simply the concept of how people interact with something. Anything that is used by people, both analog and digital, has UX. Consumers tend to gravitate toward the most convenient way to achieve their goals.
User interface design, or UI design, plays a key role in digital user experience. The UI design determines how content is laid out, proportioned, and styled, to make it user-friendly and guide people toward where you need them to go. A pleasant user experience is a great way to streamline your sales flow, 1-up competitors, or justify a higher price point.
Unless they absolutely have to, people won't use your tool if they don't like it. That goes for everything: Websites, apps, software, phones, store layouts, knives... I could go on for hours. Potential customers will choose your competitor if your competitor's website is faster, better-looking, or more straightforward. If your app has unintuitive navigation or a confusing layout, people will use it once and never touch it again.
A great user experience is not a guarantee for success, and it will not compensate for other shortcomings. Instead, look UX design as a multiplier instead of an addition: Anything greater than zero is going to see exponential levels of improvement. A great user experience enables you to guide users along the path of your choosing and set a narrative that’s most beneficial to your business.