In canon law we distinguish between:
An oath- a promise made to a human being, with God as the witness "so help me God", and
A vow- a promise made to God with a human being as the witness, such as made my a nun.
In both cases God is involved. We should be careful to distinguish between these and ordinaries promises made between human beings. An oath or a vow needs to be made with due knowledge, deliberation and freedom of will to be valid.
The sad reality is when God is left out of the equation we human beings can promise things we cannot or sometimes should not do. Which of us does not remember how President George H.W. Bush was practically crucified after promising "Read my lips: No new taxes" and then finding himself in the position, according to his best prudential judgement, of needing to raise taxes. Perhaps some think he should have followed the example of Herod.
Herod promised he daughter she could have anything she wanted, and the when she asked for something absurd, the head of John the Baptist, he felt compelled to give it to her. We can all imagine her whin, "But you promised."
We should try to be true to our word. That is a virtue. We should also choose our promises carefully. But it is also childish to expect that regardless of circumstances every merely human promise uttered should be kept. I think we can all agree that Herod should have had the courage to say to his daughter, "I don't care what I promised; the answer is no."
We human beings cannot, despite our best efforts, know the future. The often paraphrased "no plan of operations extends with any certainty beyond the first contact with the main hostile force." reflects a certain humility about human action, an acknowledgement that changing circumstances, may require a change in plans. Herod tries to use a promise as an excuse for sin. He refuses to accept that as human beings we must except moral responsibility for each choice we make, one by one. We cannot say, "Well, I promised and therefore I must."
At an ordination the bishop says, "May God who has begun this good work in you bring it to completion." At a wedding: "What God has joined no one must divide." Notice who the actor is in both cases – God. The only one who knows the future and therefore can, should and does always keep his promises.
is it simple? No. But nowhere does Jesus promise that doing the right thing would be simple.