It's said that the answer is always in the middle. In terms of parenting and discipline, too much kindness without firmness may become permissiveness and too much firmness without kindness may become excessive strictness.
It may seem like an arduous task to find a balance in our discipline, and it is! Part of the reason is because our parenting style should always adjust according to the child's developmental stage. For instance, for children between the ages of 0-12, we should tell them what to think, whereas for an adolescent (12-19), we should teach them how to think. But if you told an adolescent what to think, you should expect rebellion. It is because developmental, they are in a stage of exploration of independence/autonomy. That is not to say that we should parent without no boundaries. But we should consider how to collaborate with our teens, and at times provide options within safe boundaries.
How can we love our children through proper discipline and boundary setting? Ask for feedback from your children and loved ones, always consider the question of how 'discipline is building up your child.' Most important of all, you need to 'know' your child in order to provide intentional parenting. Those with multiple children know how different each child's temperament--what may be effective for one child may be ineffective for another. Above all, parenting and boundary setting is a question of love: how can we love our children to build them up according to their personality and development.