If you're making a consumer product, this video from Alex Zhu who made Musical.ly (later TikTok) taught me more in 30 minutes than I learned in many years watching consumer rise and fall: youtube.com/watch?v=wTyg2E

My favorite part about Alex is how succinct he is about each point he makes. I don't know if that's because English isn't his first language but, in this instance, it helps him.