How to set healthy boundries

There are two main reasons why people have problems with setting healthy boundries.
Those are:
2. Fear of abandonment / rejection
Some people let others overstep their boundries and lack the ability to set them firmly, because they're worried that if they'll set bundries, they'll be faced with abandonment / rejection, when in fact, theres nothing to truly loose. Because if anyone chooses to abandon you / reject you based on your boundries, then those people were about to stick around just to take advantage of your lack of your lack there of, those aren't people you should want around anyway.
Therefore we tend to focus on others, their needs, wants, opinions etc. more than ours, and that's why we prioritize them and their needs above our own, leading to the inability to set healthy boundries.
Therefore the key to setting healthy boundries is building self self love, self confidence and self respect. Prioritizing ourselves and in this case working on not feeling responsible for the feelings and needs of other adults and leaning into being okay with people disagreeing with us, or leaving our life if necessary, especialy if the only thing keeping them around was our inability to voice our opinions, needs, feelings and in general just set healthy boundries, since people who leave as a result of us setting boundaries are those who were most likely just sticking abound because they were benefiting from your lack of boundries anyway.
Us building a healthy self esteem leads to lower need for external acceptence, attention, validation and or love and adoration, therefore we can then set healthy boundaries without the fear of the reaction of others.