A cow is still well within the realm of dimensions that a human mind can comprehend. You won't feel insignificant when looking at a cow because while bigger, it's not that much bigger. Apart from poisoning you when you eat it, or kicking you by mistake, it has relatively little influence or impact on you, your life, your fate, or indeed, the fate of the human race.

Now, if you had a cow the size of the earth, that just sits there and eats cosmic grass, and could blow up earth and wipe out the human race with one of its farts, then suddenly the cow is rather more significant than it was before - if only because of its possible influence on you.

Finally, if the said cow is in fact not just an object but the very substrate that you exist in, and its so big that you can't even begin to imagine how big it is, and it is filled with inhuman processes that could wipe humanity out at any moment from now to infinity, then a solid sense of insignificance seems perfectly warranted.