Why did this tank have trouble holding hate?

[Jpec07]

If you pulled hate as quickly as you suggest, and they were as squishy as you suggest, it tells me that (1) they were undergeared, specifically in terms of their sword, and (2) they didn't have Grit on. Even without Grit, I've found that a single Unleash from a tank with decent gear will hold hate through at least 2-3 ticks of Regen. The same goes for an undergeared tank using Grit: a single Unleash will hold hate for a good bit longer than one tick of Regen, thanks to the relatively huge enmity modifier it has. No Grit and poor weapon? That will cause a one-tick hate-grab.

You can rest easy, though, OP: you did nothing wrong, and just happened to get paired with someone who didn't know what they were doing.

EDIT: Just saw the bit about Grit being on. The only other thing I can think is if the tank wasn't using Darkside, which is a flat boost to DPS output (and thus enmity generation). Darkside also unlocks a bunch of cooldown abilities, and gives DRKs access to Dark Arts, which will help them out substantially in their ability to both do damage and their ability to mitigate. I suspect this might be the case; one of my FC healers encountered a premade group in Sohm Al a few weeks back, and the Dark Knight was extremely squishy, wasn't using Darkside, and couldn't hold hate for crap (if you got the same group, I sincerely apologize, because it turns out they're somewhat known on our server for trolling DF healers).