the next yama is asteya, honesty. And of course it works in tandem with satya, truthfulness.
Often when we think about dishonesty, we associate it with taking something material which doesn't belong to us (stealing). Or, by doing something which is like 'taking' from another. However, asteya goes deeper than this: we can steal in other ways: by implication ie implying false harmful hints about someone, thereby stealing their mana, their personal power. Or we can imply that we have special abilities, did something special that we didn't actually do, make promises we won't/don't keep......blatant dishonesty about ourselves.
We can say & do mean things about & to people, causing stealing of their perceived integrity, their dignity. We can take credit for something good that someone else did, we can 'befriend' someone to reap the benefits that a 'friendship' would offer. The list goes on!!
The thing to remember is that the yamas are for your own benefit. Each time we knowingly do something that fits negatively into the yamas, it's like passing a shadow over the heart: over the heart of the victim & especially over one's own heart. This is not good for health, & it's definitely not good for one's state of mind.
Yoga is management of the mental fluctuations, the non-stop thoughts. How can we manage our mind when we do not manage our actions?? How can we have mental & emotional health when we do things that create turmoil in our heart & mind?
We can't. Doing this sort of behaviour, especially when acting spiritual & virtuous on the outside whilst teeming with inner turmoil, leads to conflict in our brains, & our minds. The mind races, always keeping track of poisonous behaviours, in this instance. We are not managing ourselves.
But, we do have an integrated personality & inner peace when we consciously aim to follow asteya. And developing the conscious aspect of ourselves is so important for the spiritual seeker. It's how we start to wake up spiritually. We start to become conscious in a real way. With this we develop hindsight: we realise what we have done (good, bad, or otherwise) & we see the repercussions. We start to notice how we justify grudges, non-truths, dishonesty...& we notice how these things truly make us feel. We also begin to appreciate the fruits of ahimsa, satya, ashteya. We realise how much easier it is to observe them, to become them.
If you want to sleep well at night....use the yamas, with intent. Intent is very powerful, very important. When we are intentionally dishonest, the effects for us don't seem to be as bad as when we consciously, deliberately do it. And to be able to sleep well, with a clear conscience, is a wonderful boon. We can do this when we consciously apply techniques such as the yamas.
Asteya is said to develop clairvoyance. Because we are not so cluttered within (heart, mind), & the Higher Faculties can therefore present themselves.