Trust is a key part of life - think of how important it is in your relationship, and how difficult it is to rebuild if ever doubted.
If you went to your Doctor with a sore throat and he made a mistake on the prescription giving you laxatives would you trust that Doctor in the future? You may, but more likely you would try and see another Doctor.
That is similar to work. As a manager you promise things, promise to take action to remove roadblocks, deliver development, develop talent, communicate well etc If you don't deliver or you don't explain why.....then trust disappears. People will feel that you are not the manager that they want to work for....
So build trust..under promise and over deliver!