Basically all the competitions I've taken part in. I've always thought competitions shouldn't really be about what prize you get but about the knowledge you learn during the process. Surely, sometimes you could get your confidence beaten up when engaging in these contests, which are much more challenging than textbook knowledge, at least I did, but gradually I realized it's just a part of the learning curve, and it's something unavoidable when encountering something new. I think competitions are also a great way of examining your ability to adapt your knowledge in different situations; for instance, there's a mechanism in chemistry called the SN2 reaction, it's not difficult to comprehend, yet it's changeable. Under such circumstances, it would push me to understand the principle behind this mechanism instead of just knowing "okay, this just works". So I enjoy competitions, because they "torture" me, then help me a  step forward towards academic excellence and improved mindset, much like Gandalf the Grey becoming Gandalf the White after some trebulations.