It appears that these "bad" symbols can appear whether the PC succeeds in his action or not.
But really, don't most of us impose these fluff events ANYWAY?
Like, in a lot of games, rolling a "1" means automatic and sometimes devastating failure, with consequences.
Some actions in several games also provoke attacks of "opportunity" or free attacks from the enemy. Like recklessly running PAST a foe, or loading a gun while in melee combat.
Some weapons are unpredictable (ball and chain, gunpowder etc...), and have all kinds of special rules associated with them.
In SOME games, shooting into melee might, if you miss, hit a friend instead of a foe.
Wouldn't these dice effects just replicate the kinds of things we already include anyway?
In most examples, rolling is binary: you succeed or you don't. Even with degrees of success, you can barely succeed, or nearly succeed, and so on. This new mechanic seems to extend the degrees of success idea such that you can now roll a devastating success.
For instance, perhaps your pistol shot killed the bad guy, but perhaps it also gravely wounded a comrade? If the issue was one of skill, perhaps you shot the comrade in a non-trivial locale, and the shot continued out the other side and buried itself in the enemy's face. If the issue was one of fortune, perhaps the shot exited the enemy you killed, ricocheted off of something and wounded your comrade. In the old system, you aren't prompted for results like these and so most players and GMs don't include them. Here, the dice explicitly suggest that while you can win, you might do so at a cost, which the players and GMs can narrate.