Been juggling a side business with a day job for years, so here's the balanced picture. It's genuinely doable and the extra income and skills are worth it, but it demands sacrifice and structure. Time, you're trading leisure, so make peace with that and be efficient, I use systems and batch work to avoid it eating my whole life. Legal and admin, three things, check your employment contract for conflict clauses, declare side income to IRAS because it's taxable, and consider the simplest business structure only when your volume justifies it. Do's, keep it lean, validate before investing big, keep clean separation from your employer's time and resources. Don'ts, don't let it degrade your day-job performance, that's your stability, and don't ignore tax obligations. Sustainability comes down to energy management and not overreaching. My verdict, worth it if you're disciplined and realistic, and over time it can grow into something bigger or just a solid income cushion. Just don't torch yourself trying to do everything.