A match is brightest when it’s the only source of light in a dark room (or at least it seems that way). Stars shine the brightest when the sky around them is dark and become hidden when the sun shines. A star is the most clear (and its light is the most useful/significant) when it is 1) the brightest (from the point of view of the person looking, of course), like the sun, or 2) the only source of light in the sky.

Similarly, if you want to get noticed and be significant, you either have to be the best or the only one doing what you’re doing.