
"The reason is most probably the one you have already guessed."
The thief wasn't stupid, he could easily guess that Hah'en had wanted to hide her strongest ability, the ability that gave her the upper hand. It was also an ability that was most effective when her opponents didn't know about it beforehand.
But Hah'en's mist was also not an attack ability, it was meant for camouflaging and stealth. And in a public fight in a big space such as the one she had just been in the mist wasn't as effective. Since Hah'en's opponent could just get out of the mist and wait for her to run out of steam, so to say.