Investors have always been drawn to stories. A theme, in market parlance, is simply a story with numbers attached: a cluster of allied sectors or stocks bound together by a common idea, be it the rise of renewable energy, the digitisation of banking or the expansion of rural incomes. Thematic funds promise a shortcut to tomorrow’s winners by identifying the trend before the crowd does. Unsurprisingly, they have become a fixture of the modern investor’s toolkit. Yet beneath the appeal lies a trio of difficulties that trip up even seasoned market participants.