It's easy to dismiss UX design as an expendable part of the development process, something that you could just hack around and get lucky on; because since it's easy to see when something is user-unfriendly, it must be easy to make something user-friendly instead, right? 

This article does a good job of explaining why you shouldn't underestimate the value of UX, but for the tl;dr, here are some numbers for you:

50%: the percentage of a developer’s salary that is wasted on fixing errors that a UX design process would have weeded out

75%: increase in sales in the top 2% of companies that invested in UX in a study of 408 companies. Even companies that didn't commit as much, but still invested in UX saw a 60% increase in sales

$100: the return for every $1 invested in UX

23%: the percentage of customers with a positive experience of a product that told 10 or more people about that product.