Integrity
Be honest, especially to yourself.
In order to achieve this, you need to be honest to others too. A common trap for dishonesty is to progressively believe your own lies. We often make life more complicated than need be, and being dishonest with ourselves and others exacerbates this, enclosing us in an ever-tightening web of complexity and confusion.
The best way out is to strip down to the basics. In order to know what to be rid of, or what to believe, we must be honest.
I think the taboo against stealing fits here. Stealing breaks down society and trust.
Rampant theft is either a sign of an unjust society tolerating or encouraging disparate wealth, and ignoring suffering of the poor, or a sign of lack of respect and integrity – a general moral breakdown, resulting in an distrusting and a generally less pleasant environment to live in.
Ideally of course theft should not happen, but it does and always will. In that case theft should not be necessary for survival, adjustments being made in a “just” society to make it less excusable, and it should be frowned upon and not tolerated.
Theft by definition should also include overcharging for goods and services in monopolistic environments (usually encountered when resources are scarce, or are controlled by business cartels or governments) as the consumer cannot choose where to buy and obtain a fair price.
We expend huge resources counter-acting theft including writing laws, having police forces, courts, and placing possessions in locked or otherwise secure places. We will never rid ourselves of these checks, and they no doubt employ many people, but a society can expend more or less resources on all these things, depending on how much integrity its population has.