Nowadays, we tend to go to the store (most likely a Walmart), buy and item fabricated thousands of miles away (probably halfway around the world, in China), take it home, use it a couple times and then it breaks or stops working. So what do we do? We go back to the store, buy another of the same item (since there are twenty of them on the shelf) and start the use / discard / repurchase process all over again.
During the Colonial Period and the time of the American Revolutionary War, there weren't many stores where someone could conveniently buy the items they needed. In many cases, the person had to make the item him or herself ~ or else they made do without it. That is where the phrase Necessity Is The Mother Of Invention comes in.
During the Colonial Period, when someone needed something that they could not readily purchase, they resorted to finding something that would suit their purpose. Or they would find something that could be adjusted ~ they called it jerry-rigged ~ to suit their purpose. The item shown below is just such an item that was found to suit another purpose. Necessity motivated a person to invent this item out of another.
The item above is a bullet bag in which a soldier during the American Revolutionary War carried his bullets and other shot. The bullet bag is made of leather; cloth bags would have worn and become useless much faster than leather. Bullet bags, such as this, could have been made by cutting two similarly shaped pieces of leather and then sewing them together around their edges. The sewing would have been as difficult as any other leather item being sewn, and the sewn edge would have, like a cloth bag, been more quickly susceptible to tearing open.
The necessity of finding something of leather that could be used for holding bullets and the like that was already in the shape needed, led soldiers to using animal (especially bull) scrotums. They would be tanned and the open end fitted with a wooden or bone cylinder that would enable the bag to be stoppered shut.
The picture above shows three bullet bags from the American Revolutionary War period, the one in the center and the one on the left were made the laborious way of sewing two pieces of leather together. The soldier who had either of those two bags fabricated, would have had to spend a quite a bit to have them made by someone else ~ or else he spent a lot of time and effort making them himself. The one on the right, being the one illustrated at the top of this post, was the product of necessity, and probably cost very little to the soldier.