Hundreds of years ago, it wasn't an uncommon sight to see castles fighting off sieges, trying to prevent invading armies from breaching their walls. Today, you might not have to fight off any literal armies, but you still have your own castle to defend - your website.
Web security is one of the most vital things for your business to get right. If your website is your castle, then hackers are today's invading armies, looking to breach your site's walls to access the treasure within. It's your job to fend them off, because if you don't, they can cause serious damage.