Hair

"All great events hang by a hair. The man of ability takes advantage of everything and neglects nothing that can give him a chance of success; whilst the less able man sometimes loses everything by neglecting a single one of those chances."
--Napoléon Bonaparte,
Letter to Minister of Foreign Affairs, Passariano (September 26, 1797), as quoted in Napoleon as a General (1902) by Maximilian Yorck von Wartenburg, p. 269