.. makes us stronger (Nietzsche 1844). This is pretty much underlying principle of ironman training, though it is perhaps not a good idea to push yourselves too close to the limit, since for most of us it is a hobby and not a matter of life and death.
What is certainly true is that the achievement in finishing an ironman race to the best of ones abilities can inspire confidence and a sense that one can overcome all sorts of adversity. Achieving your goals in an IM race will involve a significant period of sustained suffering which is in turn built upon a solid foundation of regular and prolonged training, and further suffering. The reward comes not only in that endorphin euphoria of the finish, and the restless night that often seems to follow race day as you lie with aching legs and sunburned and chafed limbs, but in the knowledge that you set out to meet a challenge, followed through with your plan and delivered.
These are important life skills that do you well in a whole host of other scenarios whether it be managing an injury or illness, setting out on a new business plan or indeed learning a new skill. Taking and applying that perseverance to your life challenges, and the knowledge that you know how to carry out your plans and deliver are valuable attributes. Ironman therefore can teach you how to be better at that which you choose to do, you just need to remember the lessons it teaches you.