Truth is easy when the question is about your own involvement in something. You just don't lie and don't intentionally deceive. This isn't about technical arguments, or moral quandary, or ambiguous situations, it's about marketing yourself in a world where you are expected to lie about your accomplishments to look better. Citing metrics you know are not accurate, but make you look good. Overselling your own involvement in a project. Up-selling the impact of a project by not disclosing the parts you know would undermine your perceived competence.