Legge's translation of the third line reads that the third six, divided, shows a one eyed man who thinks he can see, and a lame man who thinks he can walk well, one who treads on the tail of a tiger and is bitten, an outcome the text names plainly as ill fortune. Unlike the first two lines, this is the point in Treading where the tiger's tail is actually stepped on, and the bite that follows is the hexagram's clearest statement of danger realized rather than merely risked.
Six, divided, occupies the topmost place of Dui, the lower trigram, directly beneath the ruling strength of Qian above, and a yielding line in this exposed, boundary position is read as poorly matched to the test it faces. The one eyed man who believes he sees and the lame man who believes he walks well describe overreach born of misjudged capacity, confidence that outruns the ability actually available, precisely the condition under which treading near real strength turns dangerous.
Set against the second line's quiet, level path, the third line's bite is the direct consequence of pressing forward into contact with the tiger rather than remaining content with easier, safer ground. Legge's text offers no qualification here; the ill fortune is the plain result of capacity mismatched to the risk taken.