Author of Requiem for a Dream, Hubert Selby, Jr. said, "Eventually we all have to accept full and total responsibility for our actions, everything we have done, and have not done."
We often tell our kids that they are totally responsible for the actions they take, but what about the actions they don't take? The quote from Selby above answers that question. Kids who choose not to complete an assignment or follow through on a promise they made to a friend are responsible for their non-actions. This is really no different for us as adults. If we don't file our taxes, there are potential legal consequences for our non-action. If we don't go to work and let someone know we're not coming in, we could lose our jobs.
Our kids will continue to learn from the actions we take and don't take. The more we effectively model responsibility, the more our kids will learn about responsibility.