...saves nine. And strengthening the button-threads is a good investment that saves you irritation later on. Sadly, because clothes are so cheap, we tend to toss rather than repair. Who teaches their kids to darn in this day and age? Well, here are some tips for those who want their clothes to last longer.
When you buy apparel, check all the seams, looking for broken stitches, loose threads, or similar weaknesses in the lines of sewing.
If you re-machine sew, you will make even more holes
Resew where necessary, by hand, using a thread of a similar type and thickness if you can. The reason you need to do it by hand is that the seams will have lots of puncture holes from the original stitching, like the perforated edge of a postage stamp. If you re-machine sew, you will make even more holes and the seams end up even weaker that they were. In the worst case, the fabric will just tear away. If you hand sew, however, you can stitch through the original holes, or make stitches longer (e.g. every other hole) to spread the strain.
Another tip is to strengthen those areas that most quickly become worn, on the inside of the garment. Old nylon-stockings or a piece of material are both good alternatives to fortify clothes from the in-side. At the elbows, knees, in the crotch and wherever you know the garment will become worn first.
In some cases tears are the result of accident, such as catching fabric on a nail or splinter. If this is the case, repair is possible but may not be invisible. Darning should be done with care and skill. You will need the same or a finger weight more thread than was used to weave the original fabric. Matching the original color is very important for a good result. Remember that darning must be worked over the weak or damaged area and into an area of strong fabric, or the repair will pull away and make the damage worse. Often, a more suitable repair method is to use a support fabric behind the tear, of a similar weight to the original, couch stitched into place.
Some companies actually would prefer that you bring back what needs repairing and they will do the job for you, in some instances for free. It may be because they feel their products should be of the best quality and therefore it is a question of honor. Having a tailor fix your favorite pair piece of clothing if the zipper breaks, is generally not too expensive; though other types of repair may cost more than the original item. Which is a sad state of affairs. Darning, for instance, is one of the hardest things to do nicely. But looking up old techniques on the internet or in old books could actually be rewarding.
Or you may just chose to use the hole as a decorative element. After all jeans with tears and holes became The Fashion Item in the 80's.