Where there is no trust, job descriptions limit the effort of workers, and managers exist dying for a chance to catch the employee slipping up. Each feels the other is out to take advantage. When developing leaders, trust is necessary for the seeds to grow. Therefore, if you assign to them a task, you have to give them the freedom to complete the tasks in the way they consider to be best. You may have done it another way, and your way may be best, but allow them to try their way, even after you've shared with them how you do it, or prefer it done.
Individuals grow through trying, assessing results, and changing the approach.
As leaders they will have to trust themselves, and their own ability to solve problems and make decisions. You give them a lot when you trust their ability to do just that. You know what has to be done, you know what is needed to get the job done, but you don't have it. It leads to frustration. In addition, they need to have the necessary authority to complete the task.