Set a specific hard target, not your best effort
'Do your best' reliably produces less than a difficult number.
Do this
Replace vague goals with specific, difficult, measurable ones you have accepted as reasonable. 'Write 500 words before 10am' rather than 'work on the book'. You need feedback on progress for it to work, so make the measure visible.
Why it works
Across hundreds of studies over five decades, specific difficult goals outperform vague or easy ones, provided the person is committed and has the ability and feedback. Difficulty raises effort and persistence; specificity removes the ambiguity that lets you declare yourself finished early.
Where it fails
It goes wrong when the goal is imposed rather than accepted, when the task is complex and still being learned, or when hitting the number can be gamed at the expense of the actual aim. Narrow targets in messy work produce narrow, sometimes unethical, behaviour.
How you’ll know
You should be hitting the target roughly 70 to 80 per cent of the time. Always hitting it means it is too easy; rarely means you will disengage.