The line can be so fine, even with all the work Angelique Kerber has done on herself and her game.
And as she hoisted her second Grand Slam singles trophy of the year (and of her career) on Saturday at the United States Open, it seemed appropriate to wind back the tape eight months to the Australian Open.
In the first round there, she faced a match point in the second-set tiebreaker against the unseeded Misaki Doi of Japan and escaped only when Doi’s shot hit the tape and fell back on Doi’s side of the net.