Silk radical on the left, the indexing component and a contracted form of 糸. The original meaning of 绩 was 'to spin hemp into thread' — patient, accumulating work — which then expanded to 'achievement'. The 纟 ties it to other textile chars: 织 weave, 编 compile, 纺 spin.
Right side 责 zé supplies the sound with vowel shift zé → jì (an older reading was closer). Pedagogically it also rhymes thematically: a 责 is what is demanded of you, and 绩 is the accumulated result. Same phonetic shape appears in 债 debt and 渍 stain.
