Very interesting thread. OK, this is just the random thoughts that occurred to me, and it is just my opinion.

Every sub is different, every Dom/me is different, every D/s relationship is different: the aims are different. Some relationships are much looser, much more based on just sexual play and fun, and not expecting true power transfer. Therefore tasks and task failure can take on a different aspect. It certainly seems to me that in setting a really hard task - long-term cum restriction, for example - the D is purposefully setting a task at which the s will eventually fail. They will keep extending the time until the s fails. Because They will enjoy meeting out the punishment, They will enjoy the distress of the sub. And the sub will accept this pushing of their limits, knowing that, however hard they try they will fail eventually, and knowing that they will eventually enjoy the punishment, however miserable it makes them: even being miserable is just part of it.

But that is when the sub is not purposefully failing: they are sincerely trying to achieve it and stretch their limits, but their D has pushed it to their fail point. It may very well be that next time, the fail point is higher: the sub may learn. Or they may never be able to extend the fail point. That`s just down to the individual and their inner strength and control. We all have a breaking point somewhere.

On the other hand, the sub may very well purposefully fail a task sometimes, but I think it will be to communicate something: it can be playful (hey, I just failed a task that You know I know You know was easy, so You know I failed it on purpose just to wind You up, now You`ve gotta do something about it, that`s pretty much the equivalent of sticking the tongue out and running), willful (I`m in a bad mood and I plain don`t feel submissive so stick this) or a statement of limits (I do not like this, it is beyond what I can accept and I refuse to do it). Now, the playful failure can be acceptable and fun: it depends totally on the level of control and obedience that is expected and agreed on within the reltionship. It can also be that the D is in someway failing their sub: the sub is possibly Topping from the bottom, there. And that is a communication failure. That option and the other purposeful failures all seem to me to indicate communication failure: the D should be aware that sometimes, punishment is not what is needed: sometimes, discussion is. And that could be very hard, and possibly punishment enough, certainly part of learning.