Three times tonight - I heard the exact same metaphor. That there is one string, that when tugged, will make everything unravel.
I heard it from my roommate. I heard it on two tv shows. Shows I arguably should not have been watching because my bible study group is doing a week of fasting - and I am fasting from tv. Because I have weak spots, and these weak spots have the ability to unravel my life. TV is something I'll go to in place of God, or friends, or to avoid important tasks.
When knitting, you really only have one string. When things start getting really complicated you throw a lot of colors or techniques in there. But it all just comes back simple loops guided by needles. And these tiny loops all add up to form a fabric. But if you miss just one of these, you have the potential to unwind your whole work to that point. Can you imagine how frustrating that it? You've been working on something particular for days, and upon completion you find out half of it needs redone. Only skilled, practiced knitters can fix these slips without letting it derail the whole project.
Life is often like that. Every little gap we find is an opportunity to either undo everything and go back several steps. Or, as we grow wiser, learn to fortify the gaps we find without letting it destroy what we've achieved so far. Or worse, ignore the need to fix it, and leave these areas wide open for anyone to tug at, and tear you down at any time.