C. F. Keil and Franz Delitzsch on Proverbs 21:26

Pro 21:26 26 One always desireth eagerly;      But the righteous giveth and holdeth not back.

Otherwise Fleischer: per totum diem avet avidus, i.e., avarus; but that in התאוּה תּאוה the verb is connected with its inner obj. is manifest from Num 11:4; it is the mode of expression which is called in the Greek syntax schema etymologicum, and which is also possible without an adj. joined to the obj., as in the ὕβριν θ ̓ ὑβρίζεις (Eurip. Herc. fur. 706), the Arab. mârâhu miryatn: he had a strife with him. Euchel impossibly: necessities will continually be appeased, which would have required תּתאוּה or מתאוּה. The explanation also cannot be: each day presents its special demand, for כּל־היּום does not mean each day, but the whole day, i.e., continually. Thus we render התאוה with the most general subject (in which case the national grammarians supply המּתאוּה): continually one longs longing, i.e., there are demands, solicitations, wishes, importunate petitions; but still the righteous is not embarrassed in his generosity, he gives as unceasingly (cf. Isa 14:6; Isa 58:1) as one asks. Thus the perf. is explained, which is related hypothetically to the fut. following: though one, etc.