A fresh week, month or year offers a convenient opportunity for perspective-taking and a more rational assessment of work done to date. Letting go is hard, but iterative time segments with built-in pre-commitments around milestones can offer everyone a clean break from the past.

Behavioural Insights Team did this, setting a self-destruct button on the whole project if they weren't able to achieve a measurable outcome by a certain time.

Where in your projects can you create a future line in the sand upon which you can all decide to continue or not?