Is initiating an offer to give a female colleague a ride home considered an unbreakable promise, and is failing to attend a pre-arranged medical appointment with a doctor considered breaking a promise?

Fulfilling a promise is one of the noblest virtues. However, according to the majority of scholars, it is not obligatory to fulfill a mere promise. But if the promise entails an obligation that harms the promisee, then the preponderant opinion is that it is obligatory to fulfill it, based on the hadith: "There should be no harm nor reciprocal harm." Based on this, there is no sin in retracting the offer to drive a colleague or a doctor's appointment, unless the doctor incurred a financial obligation due to the booking, in which case he must be compensated for the harm.