In this poem, Kipling's speaker personifies triumph and disaster. He calls them imposters as both of these events don't last long. The small triumphs of life indeed taste sweet. But, staying in the hallucination of victory is an addiction and enslavement. When disaster or failure comes, the mind remains in such a state that it becomes tough to face it. Interestingly, defeat doesn't last for a long time too. That's why both triumph and disaster are traps in themselves.