Some doubt the authenticity of this fragment, claiming that is just a paraphrase of other fragments.  Punctuation is also a problem: Kahn reads, "Thinking well is the greatest excellence and wisdom: acting and speaking what is true, perceiving things according to their nature."  I think this is inaccurate.  Heraclitus is redefining two terms of popular usage: ἀρετὴ(virtue) and σοφίη (wisdom).