For a very long time I thought high self-esteem was one of the most important attributes a person could cultivate. That's not to suggest that it has no value, it's undeniably significant. The problem is, that sometimes it comes with no basis e.g. either the individual has over-estimated their abilities and has many reasons to feel modest about their achievements, or the "confidence" is actually nothing more than a front for feelings of low self-worth.
Instead, over time, I have come to believe that self-acceptance is what it's really about - it allows for shortcomings, failings, mistakes, "faults". We recognise unlikeable characteristics within ourselves, which we may think of as weak or "bad", and we accept ourselves in spite of them. You see, we all have them - yes, you too - all human beings, all imperfect, and yet we spend much of our lives striving for perfection, trying to hide those parts of ourselves, or deluding ourselves that they don't exist. We project them on to other people, because it's easier than acknowledging them as part of us. When was the last time you wound somebody up because you wanted to annoy them? And if you examined your motivations closely, was it only "just a bit of fun"? Hmmmm.........Wonder what that means about you?
The thing is, self-acceptance doesn't mean not behaving badly, but it does mean taking responsibility for it when you do. And ultimately you are less likely to behave unkindly if you genuinely know and accept that part of yourself - you can explore and find more constructive outlets for your anger/jealousy/sadness/hatred/whatever - but you have to first acknowledge and confront it's presence, which sometimes is not pleasant. The real conundrum is, without self-acceptance, I don't see how you can have true self-esteem.