An open loop is anything your mind keeps reminding you about: the call you need to make, the email you have not answered, the decision you keep postponing.
The loop may not take much time by itself, but it keeps asking for attention. That is why a day can feel mentally crowded before it is physically full.
Close or capture
For each open loop, choose one of two actions. Close it now, or capture the next action and a time when you will handle it.
A vague note saying deal with this later does not close the loop. A specific action such as call Sarah at 2:00 gives your mind somewhere to put the problem.
Finish something small
Do not start by trying to clear everything. Close one loop that has been consuming attention. Then return to the highest-value work.
Completion creates space. Space makes execution easier.