I was wondering if the Jews have been making the universal error of "enjoying the light" from the havdala candle after making the bracha, where I think that it explicity states "AD SHEYEATU LORO" in the mishna whereas one should first look at his/her fingernails (whereby enjoying the light comes first) then make the blessing on the candle? Thank you, shavua tov

The correct interpretation of “AD SHEYEATU LORO” as explained by the talmud and the poskim is that one must be close enough to the light so as to be able to benefit from it. One need not actually benefit from the light before making the bracha (Raavad and Meiri Brachot 51b). Someone who hears the bracha from another fulfills his obligation only if he is close enough to the candle so as to benefit from its light immediately upon completion of the bracha (Shmirat Shabbat K’Hilchata 61, 23). The Kitzur Shulchan Aruch writes that one makes the bracha and then enjoys the light; the mishna brura(296,31) cites the reverse order. Each minhag is acceptable. As a general rule, if there is a “universal” custom among observant Jews, it is not an error but has a valid source.