England were the only team to exit the group stage unbeaten, having won all three of their matches.
Pakistan, by contrast, suffered a 124-run thrashing by title-holders and arch-rivals India in their opener before, just days later, upsetting the ranking in a bottom versus top contest by beating South Africa.
It then needed an "ugly" win over Sri Lanka in Cardiff on Monday to take Pakistan into the last four of a tournament featuring the world's top eight one-day international sides.
Pakistan, chasing a seemingly modest target of 237 against Sri Lanka, were facing defeat and tournament elimination at 137 for six.
But Pakistan captain Sarfraz Ahmed, dropped twice, struck a superb 61 not out and received excellent support from Mohammad Amir (28 not out) in an unbroken eighth-wicket stand of 75 that sealed a tense three-wicket victory.
"When you win ugly, you learn a lot about the team," said Arthur, a former coach of both his native South Africa and Australia. "So I guess it gives a lot of confidence."
But he said a semi-final could not be the summit of Pakistan's ambitions, with an all Asian final against either India or Bangladesh, who play Thursday, in their sights.
"The last thing I want is for us to go away now thinking that we got to a semi-final, we're okay, we've achieved, because that would be a cop-out in my mind," he said.
Pakistan certainly made had work of the chase after their bowlers had held Sri Lanka to 236 all out, with pacemen Junaid Khan (three for 40) and Hasan Ali (three for 43) doing the damage.
"Sometimes that's our strength, our unpredictability," said Arthur. "It's just we do sometimes make it difficult for ourselves."
Well though Sarfraz batted, he needed the support of Amir, primarily a left-arm fast bowler.
Now back in the side after a ban and jail term in a British prison for spot-fixing, Amir is becoming an ever more important member of the Pakistan team and Arthur said: "He showed what we know he can do with the bat yesterday (Monday)."
Sarfraz, meanwhile, probably wishes he could bt at Cardiff all the time, with the wicket-keeper having made 90 on the same ground last year as Pakistan chased down a target of 303 against England in a four-wicket win that prevented a 5-0 ODI series whitewash.
"We won that time, we chased 300, so definitely our confidence is very high playing in Cardiff," Sarfraz said after Monday's thrilling triumph.
SQUADS: England Team: Jason Roy, Alex Hales, Joe Root, Eoin Morgan(c), Ben Stokes, Jos Buttler(wk), Moeen Ali, Steven Finn, Liam Plunkett, Mark Wood, Jake Ball, Jonny Bairstow, Sam Billings, Adil Rashid, David Willey
Pakistan Team: Sarfraz Khan (c and wk), Ahmed Shehzad, Azhar Ali, Babar Azam, Faheem Ashraf, Fakhar Zaman, Haris Sohail, Hasan Ali, Imad Wasim, Junaid Khan, Mohammed Amir, Mohammed Hafeez, Shadab Khan and Shoaib Malik.
Ben Stokeschampions trophy 2017England vs Pakistaneoin morganICC Champions Trophy 2017Joe RootLive Cricket Scorelive scoreMickey ArthurSarfraz Ahmed
First Published: June 14, 2017, 9:03 AM IST