Deadlines or timelines or Estimates or a little complex story points or even more complex EPICs.
These are not just jargons these are those words which gives you motivation and goals to do different tasks and achieve them on time.
These act as enablers when we want to decide where to stop on a feature, we just look up to the remaining time and decide whether we should work on that or not.
These act as disablers when we get overwhelmed with the ideas tasks and different kind of features popping up after the freezed requirements. These deadlines help us not to get swayed away from the main task at hand. It disables all the distractions.
How to use these as disablers and enablers is an art which comes through experience. No shortcuts. Hard earned pure struggle with live environments. The person who utilizes this well is termed as good engineer and the other one not so good.