When does the pride of a champion and the refusal to back down from a challenge do more harm than good? When does it become clear that the massive investment of time, energy and effort is not paying any kind of dividend at all?
These, and many other questions, will once again ring around the echo chamber in Andy Murray's mind as he tries to plot a path towards one last hurrah at Wimbledon this summer. While the rest of us ask ourselves, 'is it really all worth it any more?'
One thing is clear, as a former world number one and triple Grand Slam winner, Murray has earned the right to call time on his career whenever he likes.