Every human being must have boundaries in order to have successful relationships or a successful performance in life.

When we begin to set boundaries with people we love, a really hard thing happens: they hurt. They may feel a hole where you used to plug up their aloneness, their disorganization, or their financial irresponsibility. Whatever it is, they will feel a loss. If you love them, this will be difficult for you to watch. But, when you are dealing with someone who is hurting, remember that your boundaries are both necessary for you and helpful for them. If you have been enabling them to be irresponsible, your limit setting may nudge them toward responsibility.
Henry Cloud

I found the following book helpful
Boundaries: When to Say Yes, How to Say No to Take Control of Your Life by Henry Cloud and John Townsend

Having clear boundaries is essential to a healthy, balanced lifestyle. A boundary is a personal property line that marks those things for which we are responsible. In other words, boundaries define who we are and who we are not. Boundaries impact all areas of our lives: Physical boundaries help us determine who may touch us and under what circumstances — Mental boundaries give us the freedom to have our own thoughts and opinions — Emotional boundaries help us to deal with our own emotions and disengage from the harmful, manipulative emotions of others — Spiritual boundaries help us to distinguish God’s will from our own and give us renewed awe for our Creator — Often, Christians focus so much on being loving and unselfish that they forget their own limits and limitations. When confronted with their lack of boundaries, they ask: – Can I set limits and still be a loving person? – What are legitimate boundaries? – What if someone is upset or hurt by my boundaries? – How do I answer someone who wants my time, love, energy, or money? – Aren’t boundaries selfish? – Why do I feel guilty or afraid when I consider setting boundaries? Dr. Henry Cloud and Dr. John Townsend offer biblically-based answers to these and other tough questions, showing us how to set healthy boundaries with our parents, spouses, children, friends, co-workers, and even ourselves