Full Idea
They do not understand how that which differs with itself is in agreement: harmony consists of opposing tensions, like that of the bow and the lyre.
Gist of Idea
A thing can have opposing tensions but be in harmony, like a lyre
Source
Heraclitus (fragments/reports [c.500 BCE], B051), quoted by Hippolytus - Refutation of All Heresies 9.9.2
Book Reference
'Ancilla to the Pre-Socratic Philosophers', ed/tr. Freeman,Kathleen [Harvard 1957], p.28
A Reaction
Like squabbling couples who resent outside intervention. The remark suggests the virtues of 'dialectic', and may get to the heart of what philosophy is.