Humans are a social species. There is pretty compelling evidence that without cooperation, people are much less likely to survive and thrive.
But before people will want to cooperate with you, they will need to know that you will reciprocate. People are vigilant observers of others’ behaviors. We note when someone is a cheat, when they are dishonest, or when they are cheap. We also notice when they share, when they pull their weight, and when they are genuine. We selectively cooperate with those who are themselves good cooperators. So, in order to be in productive cooperative relationships with others, we must demonstrate that we are good teammates.
But we need not even be consciously aware of this strategic cooperative machinery driving our behavior. Instead, we usually only notice the proximate gears that drive our behavior. We notice the guilt and shame we feel when we betray someone. We feel queasy when we fail to act fairly. We feel a loss of self-esteem when we recognize that we have been lying. Whether these drivers of honesty are hardwired into our brains or whether they are products of cultural evolution is still a matter of debate, but there does seem to be a compelling case that we humans, at least the majority of us, have evolved a tendency toward honesty, not deception.