What is the best thing to start reselling?

So, I'm curious - when it comes to reselling, what's the ultimate product to get started with? Is it something that's in high demand but low supply? Or perhaps a niche item that can fetch a hefty profit margin? What factors should I consider when making this decision? And more importantly, how can I ensure that I'm not just jumping on a fleeting trend, but rather investing in something that has long-term potential? It's all about finding that perfect balance between profitability and sustainability, isn't it?