I've found my "not doing" list is a bittersweet asset; it helps me explain past decisions and puts current activities into an historical and hopefully strategic context, but it also reminds me of my personal limitations.
For individuals understanding what I "can not do" is more instructive than what I "will not do", but organizations with money to invest often feel that they "can do" anything. What they choose to do, and whether they should do those things, is the rock that product managers get to move up hills. It's the "not doing" list that prevents that rock from rolling back on top of you.
How like a winter hath my absence been
From thee, the pleasure of the fleeting year!
What freezings have I felt, what dark days seen!
What old December's bareness every where!
And yet this time removed was summer's time,
The teeming autumn, big with rich increase,
Bearing the wanton burden of the prime,
Like widow'd wombs after their lords' decease:
Yet this abundant issue seem'd to me
But hope of orphans and unfather'd fruit;
For summer and his pleasures wait on thee,
And, thou away, the very birds are mute;
Or, if they sing, 'tis with so dull a cheer
That leaves look pale, dreading the winter's near.
William Shakespeare, Sonnet Ninety Seven