If your expectations are vague, there's no possible way that you can drive accountability. And if you've ever tried to hold someone else accountable to a vague expectation, you know how frustrating it is. And you think to yourself, "We're all adults here and they committed to what needed to get done so shouldn't they just do it?"
You also don't want to be perceived as a micro-manager so you give them space. Unfortunately, this is the absolute wrong thing to do. You don't need to be a micro-manager but you do need to drive accountability to ensure that what was agreed to will be delivered on time according to the expectation that was set and agreed to.
If you're still not sure about how important of a role accountability will play for you as a leader, remember this: The people who have reached the highest level in sports, community, politics, and virtually any industry all have coaches that drive a massive amount of accountability for them.
They know that it is human nature to get distracted, to lose your way, forget what you committed to, and struggle to balance the urgent with the important.
These icons like Oprah Winfrey, Tony Robbins, Richard Branson, Hilary Clinton, Tiger Woods, and all employ coaches in part to hold them accountable.
Think of it this way, if personal accountability was easy, everyone would do everything they said they were going to do and nobody would ever miss a deadline. But, you know that's not the case which is why you need to drive accountability with your team to help them be more productive.