One has next to no experience; the other is a master. The master will
build a better looking, stronger chair, and use less wood, fewer
fasteners, and less glue in the process. This is the equivalent to the
"level v. level discount". BUT... The beginner will have very limited
tools, while the master will have a whole shop full; this is
equivalent to the "focus" discount.
The Catapult Metaphor: Suppose, as a medieval artillerist, you want
launch a firebomb over the wall of a castle. If your catapult doesn't
have enough range and lift, you will NEVER get the bomb over the wall;
this is equivalent to the basic phenomenon of Kremm Resistance. If you
WERE to get the firebomb over the wall, it would cause significant
death and destruction, but since you don't have enough lift, all it
does is crash into the wall. The wall isn't flammable, so the bomb
doesn't do nearly the damage it would normally do, but it is still a
heavy object hitting the wall at high speed, so it does SOME damage.
This is equivalent to the phenomenon of Kremm Ablation.
How Spells Work: A Wizard decides to cast a spell. He pulls out one
point of his personal kremm, and weaves a rough framework of the
spell, including, if the spell requires it, throwing an ectoplasmic
tendril (or some such) to the target of the spell. It is at this point
that he will get the legendary "bad feeling", if his current kremm is
lower than the target's. If the wizard gets the "bad feeling", he can
go ahead and finish weaving the spell, but it is, at this point, a
broken spell; as soon as he got the "bad feeling", he knew it would
never do what it was supposed to do, so essentially all he is doing is
throwing spell fragments at his target's kremm.
Now, back to your question: The master carpenter does not HAVE to use
his fancy tools, nor does he have to build the best chair he can; he
can slap together a sub-standard chair if he wants to. By analogy,
then, the higher level wizard can decide, once he gets the "bad
feeling" and knows that the spell won't work properly, to cast the
spell at its full book cost, in order to make the broken spell
fragments that he throws at his opponent's kremm as big as possible.
Two things occur to me, here: The first is that, if a wizard gets a
"bad feeling" and decides to abort the spell, he should probably still
be out ONE point of kremm. The other is that, just as the artillerist
could shift from launching fire bombs to launching rocks (or
explosives), in order to do the maximum damage to the wall, there
really ought to be a first level "Ablate Kremm" spell out there, that
DOES allow wizards to use all of their skills and tools in the process
of beating down the other guy's kremm.