If a task needs doing, do it now, rather than wait until the situation becomes progressively worse and finally out of control. For example, sew up a small hole or tear in a piece of clothing, thus saving the need for more stitching later, when the hole has become that much larger.
This, of course, is a typical English proverb promoting the Anglo Saxon work ethic. Many such proverbs encourage immediate effort as superior to putting things off until later. Examples: procrastination is the thief of time, the early bird catches the worm, an ounce of prevention is worth a pound of cure, and there’s no time like the present.
The ‘stitch in time’ notion has been part of the English language for a very long time and is first recorded in Thomas Fuller’s Gnomologia, Adagies and Proverbs, Wise Sentences and Witty Sayings, Ancient and Modern, Foreign and British, 1732, as:
“A Stitch in Time May save nine.”
Fuller’s explanation for this one supposes that because the saying is so close to a rhyme people will remember the phrase longer than if it were straight prose.
Why stitches and why nines? Most sources refer to stitches as in knitting, sewing or needlepoint. If you drop a stitch and do not fix it immediately, you will have to redo your work later. As for the “nine,” it very nearly rhymes with “time.”
Some have suggested that the term originates at sea which seems to make sense as a quick stitch to a sail that is coming apart will certainly save a lot of trouble later.
A stitch in time might only save three or six stitches. Or it might save more, like eighteen or twenty-seven. A mathematician could perhaps have fun with this idea.