If you tell a client you will do something and then you don’t do it, you will sooner or later lose that client. Your dependability will be questioned.
Think how many times over the last six months people have told you they would do something and then failed to do it. If you do that same thing twice, even over a year or two, you will be deemed at first blush to be undependable.
That is a giant step toward being viewed as not trustworthy.