The Thinking Behind The Tweet

People who have a thorough understanding of themselves do better as business leaders. They understand their strengths and weaknesses; they understand their desires and goals, they understand their internal drivers and their behaviour; they understand their attitude toward and their reactions to situations and other people. 

And, according to Wikipedia...

The Ancient Greek aphorism "Know thyself" (Greek: γνῶθι σεαυτόν, transliterated: gnōthi seauton; also ... σαυτόν ... sauton with the ε contracted), is one of the Delphic maxims and was inscribed in the pronaos (forecourt) of the Temple of Apollo at Delphi according to the Greek periegetic (travelogue) writer Pausanias(10.24.1).^[1]

The maxim, or aphorism, "know thyself" has had a variety of meanings attributed to it in literature. The Suda, a 10th-century encyclopedia of Greek knowledge, says: "the proverb is applied to those whose boasts exceed what they are,"^[2] and that "know thyself" is a warning to pay no attention to the opinion of the multitude.^[3]

In Latin, the aphorism is generally given as nosce te ipsum^[4] or temet nosce.^[5]