Because
a whetstone is no kervyng instrument, yet it maketh sherpe kervynge toolis.
From Chaucer’s blog, GALFRIDUS CHAUCERES LYNES OF PICKE-VPPE.
Yf thou were a latyn tretise ich wolde putte thee in the vernacular.
[…]
Woldstow haue me shyfte thyne voweles?
[…]
Makstow a pilgrymage heere often?
[…]
By my soule, thou art a verye mappe of helle. For thy face lyk the rivere Styx wil make me swere oothes neuer to be fforsworn, and thy embrace lyk the Lethe shal make me foryet al else, and lyk vnto the Flegeton thyn arse ys ON FYRE!
XD