Wisely spoken as someone who has lived some life, seen light and shade, happiness and sadness and everything in between. It's the way life goes.
I think, and I speak from my own perspective here, that those jet black threads merely give contrast to the colourful ones and makes them pop out a little more than otherwise they would.
Life has no recipe for success...it's just life. I like to think I can exert a little influence, shape it my way, but I like that it's also a little unpredictable. Like you suggest, if we hadn't lived our past, we wouldn't be who we are in the present and wouldn't be able to combine the two for our futures.
Thanks for your comment Ms. M, and I hope you've been very well.