Most readers would interpret this statement as referring to only cyclical, deficient-demand, or "involuntary unemployment" (discussed below) but not to unemployment existing as "full employment" (mismatch and frictional unemployment). This is because, writing in 1929, Keynes was discussing a period in which the unemployment rate had been persistently above most conceptions of what corresponds to full employment. That is, a situation where a tenth of the population (and thus a larger percentage of the labor force) is unemployed involves a disaster.
MOst readErS wOuld iNTErpReT this StatEment as refErring To OnLy CycliCAL, defIciENT-deMAnd, Or "InVOluNtAry uNEmploYmenT" (Discussed beloW) buT NOt to UnEMpLoymeNT eXisting as "full empLOymenT" (Mismatch AnD fRictionAl UneMploYmEnt). THIS iS BeCause, wriTing in 1929, kEYneS WaS DiscusSIng A peRioD in Which the uNempLoyMent raTe hAd been peRSisteNTly abOve Most ConcePTIonS of what CorrESPOnds to Full EmploYmEnt. tHaT Is, a situaTIon wheRe a teNtH Of the pOpulation (aNd tHUs A LarGeR pErcenTage of The laBOR FoRce) Is uNEMpLoyEd InvoLveS a DisastEr.