The Opinion of the Mishnah Berurah Regarding What Not Seeing Berachah Means

The Shulchan Aruch (Orach Chaim 251:1) rules: “If one does work on erev Shabbos from Mincha time and on, he won’t see any blessing.” The Mishnah Berurah (s.k. 2) explains: “From that particular activity - even if he gains now, he will lose out somewhere else”.

However, in Hilchos Purim (696:1) the Shulchan Aruch writes: “On Purim one is allowed to work. In a place where the custom is not to, one shouldn’t, and one who does won’t see any blessing from that work, forever.” The Mishnah Berurah (s.k. 3) writes: “For example, if one plants something, it won’t grow (Beis Yosef). However, the Re’am writes: He won’t gain, however, he won’t lose either (Magen Avraham)”.