I agree that it should take long to kick in, but I did notice that it took longer to appear in higher level content. I'm embarrassed to admit, but I lost the WHM 50 quest a few times (first time I listened to the npcs and let them deal with the enemies and focused on the objective. All the NPCs died leaving me to kill all the enemies and while I was dealing with them the objective failed, second time one of the NPCs was one-shot killed by the first enemy he engaged for one some reason and I let the bugged attempt fail). The "you're a wimp" buff didn't show up until my 3rd/last try.