Literally, wood will burn even if drawn through water, and the willow will droop if sown out of season. Figuratively, natural will and inclination will predominate and exhibit themselves, although submitted to the most antagonistic influences.
Birth's gude but breeding's better.
Bitter jests poison friendship.
Black's my apron, and I'm aye washing 't.
When a man has got a bad character, although he may endeavour to redeem it, he will find great difficulty in doing so.
Black will tak nae ither hue.
Blaw the wind ne'er sae fast, it will lown at the last.
Blind horse rides hardy to the fecht.
"Who so bold as blind Bayard?"—French.
Blind men shouldna judge o' colours.