The default theme doesn’t visually distinguish links to nonexistent pages from links to existing pages, so if you mistype a link you won’t know it’s wrong unless you click on it. I had a bunch of wrong links on my user page (didn’t realize capitalization mattered) and only noticed when I tried on a different theme (Simple) & suddenly a bunch of them had strikethrough.
The Teahouse theme (which works so much better on my phone!) doesn’t distinguish either.