Even then it's far more complex. Using football as the example rather than rugby, if a team is winning with minutes to go you'll often see them taking the ball to a corner flag and trying to kill the game, rather than still "playing as if it's nil-nil". On the other hand, there are times when a team who has a lead will adapt to defend the lead (changing tactics, taking off attackers and replacing them with defenders, etc.), will then concede a goal, and will end up worse off than if they'd kept the offensive strategy that gave them the lead.