[CSteefel]

Originally Posted by Morthoron

As far as level of courage, that also is not really the main quality necessary in defeating a Balrog, is it? Gandalf felt the Balrog was beyond the strengths of Aragorn, Boromir, Gimli and Legolas, and I don't think you could question any of their courage. No, a Balrog crushed the dwarves in Moria, and it wasn't because the dwarves lacked courage, it was because they did not possess the inherent power (born of Valinor) necessary in counteracting a Balrog.

I think this is a good point. If you look at other cases where Dwarves or Men encountered Balrogs, there is often explicit mention of the great fear engendered by the encounter. In the case of Dain in the War of the Dwarves and Orcs, we hear that Dain comes down from the Gate after slaying Azog (Appendix A):

...it is said that when he came down from the Gate he looked grey in the face, as one who has felt great fear

and Dain goes on to explain further when he says to Thrain

But we will not enter Khazad-dum. You will not enter Khazad-dum. Only I have looked through the shadow of the Gate. Beyond the shadow it waits for you still: Durin's Bane. The world must change and some other power than ours must come before Durin's Folk walk again in Moria.

Of course, Dain's words are prophetic here, since it is Gandalf (a Maiar) who finally defeats the Balrog and rids Moria of it.

Similar thoughts come from Aragorn when he mentions in the Fellowship of the Ring that in fact he had passed once into Moria, through the Eastern Gate:

'I too once passed the Dimrill Gate,' said Aragorn quietly; 'but though I also came out again, the memory is very evil. I do not wish to enter Moria a second time.'

Clearly, there is something much more than the physical prowess (or stealth) of the Balrog here, so it presumably requires a being with spiritual powers well beyond those of either a Dwarf or a Man.