Here are 5 mistakes I made as a Product Manager (among several others!):
1. I unintentionally made myself the customer by taking decisions based on personal bias, preferences & "gut" assumptions.
Lesson: Talk to customers & look at the data.
2. I was insecure to admit to the team that "I didn't know" something. Thus, I'd force some interpretation of the data & deliver a verdict.
Lesson: It's OK not to know something. It promotes your desire to actually research, survey & experiment to become more informed.
3. I thought copying the user experience, design aesthetic & user flow of an established product would work like a charm on mine.
Lesson: Every product is unique in some way. While you can certainly use inspiration from others, execution always requires a tailored approach. Also, don't always let the status quo influence your own creativity.
4. I focused more on cranking out a lot of features (without a go-to-market plan) & ignored optimizing existing ones.
Lesson: Throwing features at users without a plan to educate/onboard them is a recipe for doom. Also, don't abandon a feature after release.
5. I'd prioritize features based on the "loudest" voices in the room.
Lesson: Establish a common, objective criteria to assess the value of a user story.