It's not in any coaching manual, in anyone's kitbag or on the scoreboard, and it wouldn't register with thermal cameras, super-sensitive microphones or ball-tracking gizmos.
But it's as important to success on the cricket ground as runs, wickets or anything else. Maybe more so. And, every few years, it's rebuilt from the ground up.
It's the relationship between coaches and their players - particularly the senior figures in the team and, at the head of that queue, the captain.
South Africa are in that moment now: Ottis Gibson, Russell Domingo's replacement, is scheduled to arrive in Mzansi tomorrow.Then the rebuilding will begin .
"The captain and the coach are trying to get the same message across, and that breeds confidence," Domingo said. "If varied messages are coming across, it can create uncertainty about how to go about things.
"It's probably the most important relationship in the group - to make sure the two of you stay unified even when things are not going well. So that you always come across in a controlled, calm manner and are always supporting each other when there are tough situations around."The bond needs compatibility if it is even to form properly, never mind grow and strengthen.
"There's no doubt that the better you get on personally with the coach or the captain the easier it is to buy into his understanding and reasoning, whereas if the mutual respect isn't there it's very easy to find fault and criticise and cause conflict," Domingo said.
Then what?
"The team is more important than the relationship between the coach and the captain. So if there is disharmony, you've both got to be professional enough for that not to be exposed in front of the team or in a public space."The core leadership of the team are really good people," Domingo said. "They all have good value systems, they all try to live in professional and disciplined ways."
He rattled off names to bolster his point.
Among them was that of AB de Villiers, who has opted not to play in South Africa's last 15 tests but will be back in whites against India and Australia in the new year.
Captain Faf Du Plessis himself has said the test team didn't expect to see De Villiers again, which might make for an awkward reunion...