What does it mean that written commitments outperform mental commitments?

Putting a commitment in writing makes it concrete and reviewable.

Example: You tell yourself on Sunday night that you'll run three mornings this week. By Tuesday, you've already renegotiated the terms — maybe two runs, maybe evening instead of morning, maybe this week isn't ideal. Now try the alternative: you open a notebook and write 'I will run Monday, Wednesday, and Friday at 6:30 AM before coffee.' You sign it. You put the notebook on your nightstand. Wednesday morning when the alarm fires and you want to skip, the negotiation feels different — you're not debating a vague intention, you're deciding whether to contradict a specific, physical, signed statement in your own handwriting.

Try this: Choose one commitment you've been carrying only in your head — a behavior change, a project deadline, a promise to yourself. Write it down on paper in specific, concrete terms: what you will do, when you will do it, and what counts as completion. Sign it and date it. Place it somewhere you'll see it daily. At the end of seven days, assess: did the written version hold better than the mental version typically does? Notice what changed — not in your motivation, but in the psychological cost of defection.