Board Thread:General Discussion/@comment-31371445-20170222233857/@comment-31536324-20180910013246

To THA

Exactly, in addition to that, the measurement only really works in regard to SOUL Power. Since it and DT are clearly differentiated as two different things, and SP is what's outright stated to be what's locking the barrier, the metric can't work for DT since - unlike SP - it CAN fluctuate up or down in terms of quantity.

It also wouldn't make sense if one species can have DT Fluctuations and the other can't; that's like saying fish can swim but humans can't. And given all of the evidence - Frisk being most associated with DT, them and Chara having red SOULS, both the red flags, the plaques, the Alphys Entries, the Omega Flowey and GoHD fights, and the differences in Frisk between the Pacifist, Neutral, and Genocide Routes - it seems rather clear that, even without direct quotation, the Red Trait is Determination. But even then, a direct quotation wouldn't be as satisfying as actually finding all the hints and clues and figuring it out for yourself.