Influence without authority: A lot of jobs (especially product ones) are dependent on influencing people or driving alignment without authority. I think it boils down to data, emotion and ego. Here's what I've learnt so far, and some best practices to do so:
1. Have zero ego: 'I'm the expert' or 'I think this is right' is bad. Irrespective of who you're talking to, go with 'I don't know, but this is what I have learnt so far'. With ego, the discussion is finished before it even begins. Talk about the 'why'; which brings me to
2. Explain the why as deeply as possible: Data is the best way to do this, if you don't have data, use a proxy and build arguments and ladder up on the basis of this data and first principles. Sometimes you don't have facts, which brings me to
3. Appealing to emotion: If you don't have data, appeal to emotion. Its counter-intuitive, but it might be helpful to frame arguments against yourself, until you get to 'that's right' from the other person. This will precisely identify the bit of your argument they disagree with
4. Don't disagree and commit: I personally do not like it, as it festers over time. Some folks wear it as a badge of honour though. If you and your stakeholders absolutely cannot agree on something, *respectfully* escalate or get a 3 P view; which brings me to the last one
5. Do not threaten or accuse: 'I will talk to your manager'/'Why don't you ever understand'/'Why are you so difficult' are garden variety accusations that are full of biases, bad intent and should not be done.
Any other tips I should know of?