Get in the habit of asking a lot of questions
Question all your assumptions and determine whether you need to check your facts. If you are, as a UX designer or researcher, constantly on the lookout for threats and potential points of failure, you and your products will be stronger.
This is a type of critical thinking that will serve you well at all times. You need to be aware of how much you don’t know and what that means. Remember that awareness of your own limits will allow you to be as effective as possible within them.