Safety is not directly affected by your best performance, or even your average performance. What matters, directly, is your worst-ever performance. This is called the minimax principle: make sure your worst-case performance is good enough. …
If your usual tolerances are tight enough, then even on the super-rare occasions when your performance is ten times worse than usual, you will still have a wide margin of safety.
John S. Denker
I must go down to the seas again, to the lonely sea and the sky,
And all I ask is a tall ship and a star to steer her by,
And the wheel‚s kick and the wind‘s song and the white sail's shaking,
And a grey mist on the sea's face, and a grey dawn breaking.