Most likely you think about it, though. When you're coding, and you have a triple loop, do you think, "Oh, this is O(n^3). Is n going to be too big here?"

It may be something that's so intuitively obvious to you, that you don't even think about it. So you naturally use the hashmap, where someone else might try a list and then start doing a lookup in a loop. Then while that particular instance might not break things, it'll slow things down, so overall the application feels sluggish instead of snappy.