Simulators lie about three things

Dark mode, big text and reduce motion. More people use big text than any other setting, and it's where apps fall apart.

A simulator is a picture of a phone. It is very good at showing you what your app looks like on a phone that nobody has touched. Real phones have been touched.

Dark mode

Most people leave it on automatic, so the app is light at lunch and dark at night. The Kit follows the phone, so you get this for free. What you have to check is that nothing in your app fights it, like a hardcoded white box that glows at midnight.

Big text

More people turn text size up than use any other accessibility setting. It's also the one that breaks the most apps, because a number that fit at the default size no longer fits, and slides off the screen. Turn it all the way up, once, on every app you ever build. It takes twenty seconds.

Reduce motion

Some people get motion-sick from bouncing interfaces. When they turn this on, your app should still work, with the bounce gone. If a feature only makes sense with the animation, the feature is the problem.

Every day page in the course ends with the same three checks. That's not an accident.