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Experiments reveal that the superconductors UPt_{3}, PrOs_{4}Sb_{12}, and U_{1−x}Th_{x}Be_{13} undergo two superconducting transitions in the absence of an applied magnetic field. The prevalence of these multiple transitions suggests a common underlying mechanism. A natural candidate theory which accounts for these two transitions is the existence of a small symmetry-breaking field; however, such a field has not been observed in PrOs_{4}Sb_{12} or U_{1−x}Th_{x}Be_{13} and has been called into question for UPt_{3}. Motivated by arguments originally developed for superfluid ^{3}He, we propose that a generalized spin fluctuation feedback effect is responsible for these two transitions. We first develop a phenomenological theory for ^{3}He that couples spin fluctuations to superfluidity, which correctly predicts that a high-temperature broken time-reversal superfluid ^{3}He phase can emerge as a consequence. The transition at lower temperatures into a time-reversal invariant superfluid phase must then be first order by symmetry arguments. We then apply this phenomenological approach to the three superconductors UPt_{3}, PrOs_{4}Sb_{12}, and U_{1−x}Th_{x}Be_{13}, revealing that this naturally leads to a high-temperature time-reversal invariant nematic superconducting phase, which can be followed by a second-order phase transition into a broken time-reversal symmetry phase, as observed.