Tech and marketing folks, how do you manage side hustles without burning out?

I’m an engineer with a strong interest in marketing, and lately I’ve been feeling pretty drained by the usual 9-to-5. The idea of a side hustle is appealing, but I’m wary of adding more to my plate. For those of you who’ve found a balance, how did you identify a side project that felt energizing rather than exhausting? I’m curious about what first steps you took to validate an idea without a huge time investment. Also, how do you handle the mental shift between your main job and your side work, especially when both involve tech and marketing? I’d love to hear about any low-effort strategies you used early on to test the waters. What’s one thing you wish you’d known before starting?