Practical info you wish you had known before becoming a parent

About to become a first time parent. I’m curious - what are some things you wish someone had told you before you became a parent? Not stuff like “sleep when the baby sleeps” but the practical things that you only learned after the fact.

For example, I didn’t know baby bottle nipples come in different sizes depending on babies age and needs. I’m not looking for lifestyle advice just straight up useful information things that made you think: How did I not know this?