What a great word! tenacity
n : persistent determination [syn: doggedness, perseverence, persistence, persistency, tenaciousness, pertinacity]
\Te*nac"i*ty\, n. [L. tenacitas: cf. F. t['e]nacit['e]. See Tenacious.] 1. The quality or state of being tenacious; as, tenacity, or retentiveness, of memory; tenacity, or persistency, of purpose.
Source: Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc. Dictionary.com
Louis Pasteur was quoted as saying:
Let me tell you the secret that has led me to my goal: my strength lies in my tenacity.