Ask HN: What is the ONE most important thing you've learnt on HN?

Answers can be technical (like a server config loophole you had always overlooked) or non-technical.

For me, it was to cut down on hyperbole when communicating. Before, I used to make statements like 'I am sure everyone feels the same way'. Now, I'll ask questions like, how can you quantify how many people feel the same way? Did you measure that or can you make a reference to the statement you just made?