Your boss doesn’t always follow up on promises.

Part of developing trust between bosses and employees is doing what you say you will do. Employees tend to do this well. There is only one manager to follow up with in most cases, and there is also risk to a career if lack of follow-up is a pervasive problem. Managers, on the other hand, typically have many people they are committing actions to, both up and down the chain of command. They also have obligations to their bosses, which tend to be prioritized, rightly or wrongly, above those they make to their team.