Fleixbility is a skill. If you can easily change track to a 'Plan B' when circumstances change, you will handle the complexity of family life with much less stress. A real part of the skill, though, is not being too flexible, especially in the face of resistance from your children. Yes: we will be flexible enough to sometimes offer options, listen to reasonable objections and consider sensible alternatives but, No: we are not going to be derailed from our plans just because a child doesn't want to do something. There is a time for flexibility, but there also times to stick to our guns. If your children learn that their obstinate behaviour will always knock you off-course, then you can expect obstruction all the time; but when children sense your resolve, they will often just shrug and comply.
Perseverance especially applies to changing their behaviour. If you want your children to try new foods, do chores, improve their manners, do their homework, etc., then don't be too quick to resort to a Plan B if you do not see a rapid improvement. Moving on to a new strategy too soon can feel to your child like a lack of determination. Most issues will take time to improve, and your children really do want to see you hold fast, so give your strategy time to work before you move on.