'zeal', non-laxity, earnestness, diligence, is considered as the foundation of all progress.
Just as all the footprints of living beings are surpassed by the footprint of the elephant, and the footprint of the elephant is considered as the mightiest amongst them, just so have all the meritorious qualities zeal as their foundation, and zeal is considered as the mightiest of these qualities'' (A. X, 15).
Cf. the Chapter on Zeal (Appamāda Vagga) in Dhp., and the Buddha's last exhortation: "Transient are all formations. Strive zealously!" (appamādena sampādetha: D. 16) - In the commentaries, it is often explained as the presence (lit. 'non-absence') of mindfulness (satiyā avippavāsa).