When a warrior strives and struggles in battle, their mind is already
low, degraded, and misdirected as they think:
Yo so, gāmaṇi,
yodhājīvo saṅgāme ussahati vāyamati, tassa taṁ cittaṁ pubbe gahitaṁ
dukkaṭaṁ duppaṇihitaṁ:
‘May these sentient beings be killed, slaughtered, slain, destroyed,
or annihilated!’
His foes kill him and finish him off, and when his
body breaks up, after death, he’s reborn in the hell called ‘The
Fallen’.
SN 42.3
From the sutta quote above, we see that the warrior who strives (ussahati) and struggles or exerts himself (vāyamati) in battle, is already deep in the low, degraded and misdirected mindset of killing.
Similarly, just having the fleeting thought of hurting the Buddha, killing an arahant, killing one's mother, killing one's father or causing a schism in the Buddha's sangha, is not sufficient to be considered an incurable action.
It's an incurable action only when one strives (ussahati) and struggles or exerts himself (vāyamati) to commit those heinous acts, regardless of whether he has actually been successful or not, just as in the case of the warrior in battle.
So, yes, even an unsuccessful intentional and deliberate attempt to perform these wicked acts would be incurable.
The OP asked in the comments to the effect of: What about Angulimala who killed many humans and attempted to kill the Buddha, but eventually became an arahant?
When Angulimala attempted to kill the Buddha, he did not know that it was the Buddha or an arahant. He only saw a monk walking alone along the road.
So he did not have the intention to kill the Buddha. He only had the intention to kill a monk.
It's just like the difference between intentionally killing an unknown woman who the killer did not know to be his mother, and intentionally killing his own mother knowingly. The latter carries more terrible consequences than the former.
Please read the story of Chakkhupala in the commentary of Dhammapada 1 and also the quote:
"Intention, I tell you, is kamma. Intending, one does kamma by way of
body, speech, & intellect." - AN 6.63
Karma is based on intention in Buddhism. Karma is not a universal system of justice.
The sutta below clearly shows that merely thinking about hurting Ven. Sariputta did not cause karmic consequences for the yakkha.
However, intentionally striving and exerting himself to hurt Ven. Sariputta caused the yakkha to experience karmic consequences, even if Ven. Sariputta was not successfully hurt the way he intended him to be.
This shows that striving and exerting oneself results in karmic consequences, whether or not the intended action reached its intended outcome.
And on that occasion two yakkhas who were companions were flying from
north to south on some business or other. They saw Ven. Sāriputta —
his head newly shaven — sitting in the open air. Seeing him, the first
yakkha said to the second, "I'm inspired to give this contemplative a
blow on the head."
When this was said, the second yakkha said to the first, "Enough of
that, my good friend. Don't lay a hand on the contemplative. He's an
outstanding contemplative, of great power & great might."
A second time, the first yakkha said to the second, "I'm inspired to
give this contemplative a blow on the head."
A second time, the second yakkha said to the first, "Enough of that,
my good friend. Don't lay a hand on the contemplative. He's an
outstanding contemplative, of great power & great might."
A third time, the first yakkha said to the second, "I'm inspired to
give this contemplative a blow on the head."
A third time, the second yakkha said to the first, "Enough of that, my
good friend. Don't lay a hand on the contemplative. He's an
outstanding contemplative, of great power & great might."
Then the first yakkha, ignoring the second yakkha, gave Ven. Sāriputta
a blow on the head. And with that blow he might have knocked over an
elephant seven or eight cubits tall, or split a great rocky crag. But
right there the yakkha — yelling, "I'm burning!" — fell into the Great
Hell.
Now, Ven. Moggallāna — with his divine eye, pure and surpassing the
human — saw the yakkha give Ven. Sāriputta a blow on the head. Seeing
this, he went to Ven. Sāriputta and, on arrival, said to him, "I hope
you are well, friend Sāriputta. I hope you are comfortable. I hope you
are feeling no pain."
"I am well, friend Moggallāna. I am comfortable. But I do have a
slight headache."
"How amazing, friend Sāriputta! How astounding! How great your power &
might! Just now a yakkha gave you a blow on the head. So great was
that blow that he might have knocked over an elephant seven or eight
cubits tall, or split a great rocky crag. But all you say is this: 'I
am well, friend Moggallāna. I am comfortable. But I do have a slight
headache'!"
"How amazing, friend Moggallāna! How astounding! How great your power
& might! Where you saw a yakkha just now, I didn't even see a dust
devil!"
Ud 4.4
