Promises Create Obligations, Not Forecasts
Predictions and promises both speak about the future. They do not do the same thing.
A prediction estimates what is likely to happen. A promise creates an obligation for the speaker. I think the project will finish Friday is a forecast. I will deliver my part by Friday is a commitment.
The promised outcome may still depend on conditions beyond one person's control. That is why responsible promises need scope. What exactly is mine to do? What happens if circumstances change? When must I communicate?
The power of a promise is not that language magically guarantees an outcome.
It is that speaking can reorganize action, expectation, coordination, and accountability. A prediction asks whether the future will occur. A promise asks who I will be in relation to helping bring a future about.