A bit of an aside, but for me the reference to "If" is a turn off. I read it as promoting a fairly-arbitrary code of stoicism rather than effectiveness. The main message I get is keep cool, don't complain, don't show that you're affected by the world, and now you've achieved your goal,

I agree that the poem is about stoicism, but have a very different take on what stoicism is. Real stoicism is about training the elephant to be less afraid and more stable and thereby accomplish more. For example, the standard stoic meditation technique of thinking about the worst and scariest possible outcomes you could face will gradually chip away at instinctive fear responses and allow one to think in a more level headed way. Similarly, taking cold showers and deconditioning the flinch response (which to some extent also allows one not to flinch away from thoughts.)

Of course, all of these real stoic training techniques are challengingly unpleasant. It's much easier to be a poser-stoic who explicitly optimizes for how stoic-looking of a face they put forward, by keeping cool, not complaining, and not emoting, rather than putting in all the hard work required to train the elephant and become a real stoic. This is, as you say, a recipe for disaster if pushed too hard. Most people out there who call themselves stoics are poser-stoics, just as Sturgeon's Law would demand. After reading the article you linked to I now have the same oppinion of the kind of stoicism the Victorian school system demanded.