Know How Things Are Going To Break

This is, perhaps, the evil twin of Know How to Confirm It Works.

Knowing how to confirm it works (and doesn't work) is about making sure that you have the appropriate visibility into the things you launch. Knowing how things are going to break is about understanding both the tradeoffs made in your work and how usage is going to change.

Did you design a drop down menu that works fine with 20 or so items (nobody should really need more than 5, right?) but it's not impossible for there to be hundreds of items? That might be fine, but it should be explicitly thought about and communicated.

You should know what parts of your system will slow down as certain database table get bigger. You should know what tables are growing fast enough that you might need to worry about capacity issues. You should even know about parts of the code that will grow untenably complex if more features are added to the current design.

There will always be problems that are hard, if not impossible to forsee but spending time thinking about where you are likely to first see breakage can help you monitor these areas and get ahead before they become serious issues.