。
Caution is the better part of valor.
Literal
Caution-deepness [topic-は] courage [possessive-の] major-portion is-[である].
A direct translation of the English proverb. 用心深さ ('caution,' literally 'caution-deepness') uses the ~さ nominalization on 用心深い (cautious). 大半 ('the majority / most of'). である is the formal written copula.