Speaking of your peers, there will be times when you and your peers (particularly across functions — i.e., your product or business peers) will need to act together to say no. This can apply to a no at any level. Sometimes you will use your technical authority to say no in a way that is beneficial to the product team. Sometimes you will appeal to the finance department to help you say no to certain budget excesses. Playing good cop/bad cop can be a little bit dishonest, so use this sparingly, but it can be useful to lend your authority to a no and then be able to call in the favor when you need support for your own no in the future.