Non est ad astra mollis e terris via (Lucius Annaeus Seneca) The way from earth to the stars is not peaceful.
Longum iter est per praecepta, breve et efficax per exempla (Lucius Annaeus Seneca, a.k.a Seneca the Younger)
Teaching by precept is a long road, but short and beneficial is the way by example.
Errare est humanum. (Seneca the Younger, an ancient Roman philosopher) To err is human.