I didn't make that claim. What I am implying though, is that in order to be a person of integrity I do believe it takes some forethought. In the heat of the moment, when you are very incentivized to lie, everything is going to be pushing you to take the easy way out and you will. If, however, you have thought about it, and made a decision before these moments even occur, you have a chance. Even then I don't think you will always be successful.

Certainly people can change and improve themselves. I don't believe "once an x always an x" for anything I can think of.

Turns out, what I am saying is all backed up by a study which took about a minute of Googling to find: https://www.nature.com/articles/nn.4426#affil-auth

"Here we provide empirical evidence for a gradual escalation of self-serving dishonesty and reveal a neural mechanism supporting it. Behaviorally, we show that the extent to which participants engage in self-serving dishonesty increases with repetition. Using functional MRI, we show that signal reduction in the amygdala is sensitive to the history of dishonest behavior, consistent with adaptation. Critically, the extent of reduced amygdala sensitivity to dishonesty on a present decision relative to the previous one predicts the magnitude of escalation of self-serving dishonesty on the next decision. The findings uncover a biological mechanism that supports a 'slippery slope': what begins as small acts of dishonesty can escalate into larger transgressions."