Consider it done! is a research paper written by E. J. Masicampo and Roy F. Baumeister. The authors state that once we commit to a particular plan of action to complete a task, we think less about that task.

We have, on average, about 15 ongoing goals and projects at any given time, each goal with its own set of milestones. We also know unfinished goals can be a burden, so we offload them onto a to-do list. We feel relieved from the need to hold on to it mentally.