A circle's thin line divides and separates. Something is either in the circle or outside the circle.
Your website is like a circle.
Think about it.
Every decision you've made so far in terms of planning, design, code, user research and even deployment includes some people and excludes others. You've made most of these decisions without knowing it.
No alternative text to images or low colour contrast? People with visual impairments won't understand your images or won't enjoy your content.
No keyboard navigation or no form labels? People who rely on screen readers are out.
No captions or transcripts for videos? People who are deaf or hard of hearing miss out on your message entirely.
Do you have a time limit on forms with no way to adjust or pause it? People with cognitive disabilities or motor impairments may not be able to finish before time runs out.
How about that flashy interface with animations and no option to turn them off? People with vestibular disorders or who are easily distracted might feel dizzy, nauseous or overwhelmed.
Each of these decisions narrows your audience, often unintentionally.
The good news is you can always widen the circle you're building. But you have to be intentional about it.