At this World Cup, they have scrambled an escape against Nepal, scraped past Scotland and Italy when the walls threatened to crumble in, and beat Sri Lanka with one of the great one-man shows.
It is a welcome change for a side that squandered any chances they did create in Australia.
“If you can get yourself out of some tricky positions and end up winning games it does wonders for your confidence,” Jacks said.
“There’s no better team than one that fights and finds a way of winning.”
This is not to say England have been perfect by any means – nor that everything that has come this winter is forgotten.
There remains no certainty that McCullum will be in charge come the summer, even after this run to the last four.
The Test victory in Hyderabad last year, which was followed by four heavy defeats, also shows one should never get too carried away.
And Harry Brook’s men now leave Sri Lanka – a country that has provided a sanctuary for over the past weeks and returned six T20 wins from six – for India and the semi-finals.
There they could meet the co-hosts or West Indies or South Africa – this tournament’s three most-feared teams. There are only so many times you can go back to the well.
“Everyone knows about India and the storyline that brings,” Jacks said.
“It could also be West Indies and they have beaten us in Mumbai.
“We know how tricky that will be. We will watching that game on Sunday. We will be prepared. We go in with optimism.”
It is that optimism that has been drained over the recent months. For many it will, quite rightly, take months to come back.
Jacks, though, spoke with a glint in his eye – the look of a side starting to believe in themselves again – and dismissed concerns over the lack of straightforward wins.
“We’ve won six out of seven games and we’ve qualified for a semi-final,” he said.
“At the end of the day, no one really cares. We obviously want to play well in them but we’re not gutted we haven’t played a perfect game.
“That’s T20 cricket.
“What we’ve done well is the key moments – we’ve kept a calm and clear head and we’ve managed to get those rewards.”
For now it is working. It is a welcome flash back to the good times.