In a perfect way with no mistakes or imperfections.
From Old Norse 'flaga' meaning 'slab of stone' or 'crack,' combined with '-less' (without) and '-ly' (in manner). The sense evolved from having no cracks or breaks to having no faults at all.
No human actually performs flawlessly—even Olympic gymnasts have tiny wobbles that judges look for, which is why a 'flawless' performance is really about minimizing visible imperfections.
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