"Every time we design a system, we have to minimise the potential harm. Look at the code that you write, look at the systems you design, and think: How could this be abused? How could this fall apart? What are the failure states here? If you were a bad actor, if you wanted to use this maliciously, how would you go about it? Think about how you’d attack your own systems, explore those failure states, deliberately screw things up and see how your code copes. Because if you don't, someone else will."