What’s the one mistake you made with your first website that you wish someone warned you about?

Hey everyone!
I’m currently in the process of setting up some new web projects, and while reading through tutorials, it struck me how much trial-and-error goes into building a site for the first time.
Whether it's choosing the wrong plugins, picking a host that couldn't scale, ignoring basic SEO, or messing up site structure — most of us learn things the hard way.
If you could go back in time to when you launched your very first site, what is the one single advice or warning you would give yourself?
Curious to hear your thoughts and stories — hopefully this thread can help out a lot of beginners here!