We know. You want your website to look aesthetically pleasing, and whilst it might look good, it might not be the best for functionality.
UX stands for user experience, which is the overall experience of a person using a product such as a website or computer application.
You might have a cool and aesthetic website but if the layout is poor or overcrowded won't work well with the user. Having a poor layout can interrupt the navigation you want your user to take, which will be explained further down. On the other hand, an overcrowded layout with too many elements present at once can overwhelm the user, leading them to click off. Poor or overcrowded layouts can look messy and unprofessional. This will negatively affect user experience and lead them to not trust your business.
One mistake you can make when thinking about aesthetics is not investing in customisation. There are a lot of cookie-cutter websites out there, and they might look really good, but if you invest in customisation you can design to match your user behaviours whilst having an aesthetic look.