Fret the small things!
For want of a nail, a shoe was lost.
For want of a shoe, a horse was lost.
For want of a horse, a messenger was lost.
For want of a messenger, a message was lost.
For want of a message, a battle was lost.
For want of a battle, a war was lost.
For want of a war, a kingdom was lost.
All this was lost for the want of a single 8 penny nail.
In other words, small things can at times have far larger consequences than you might believe.
Via Ben Key in a comment on a different thread

Thanks for sharing. I wondered where I had seen the poem.
Actual use of this poem, by the Master Himself:
Misery is the river of the world – Tom Waits
Ben Key No, thank YOU. I hadn’t seen this little ancient tidbit before.