We present a heuristic mechanism for the origin of the unusual triplet lasing from (E)-3-(((4-nitrophenyl)imino)methyl)-2H-thiochroman-4-olate·BF₂. We demonstrate that whereas the moderate lifetime (1.03 μs) of the first triplet state (T₁) prohibits triplet–triplet annihilation, the relatively faster S₁ → T₁ intersystem crossing and the 10⁴ times ...