There are several reasons why you should never have a fear of failure as an inventor. Did you know how many times Thomas Edison tried to design a practical light bulb and failed? The answer is over one thousand times, Thomas Edison failed to make a practical light bulb before he succeeded. Sometimes failures can even be turned into inventions. Below I have listed several inventions that "failed in their intended purpose" but succeeded when the inventor realized that the failed invention could be re-purposed into something successful.
Viagra before it was Viagra, was an experimental drug explored as a solution to cardiovascular ailments. Well, it was discovered that it had a side effect during its studies as a heart medicine. It provided increased blood flow to the penis, and improved erectile dysfunction. So Viagra while failing as a heart medicine succeeded as most useful as a drug for erectile dysfunction.
So what do you do with a stale dried up cereal paste. Doctor John Harvey Kellogg invented Corn Flakes cereal. However, corn flakes were invented as a result of Kellogg's attempt to save a ruined dish of boiled wheat. Kellogg over-boiled his wheat, and then forgot about the pot sitting on the stove, making both a dried up and stale wheat paste. Kellogg rolled the paste out and cut it into pieces which he toasted, it was delicious, and after experimenting with the process he tried the same thing with over-boiled, stale, corn paste. And Kellogg's Corn Flakes were born.
Before it was Ivory Soap, it was simply called the White Soap, and it didn't, as the trademarked logo describes, float. Until one day in 1879, a hungry employee eager for his lunch, forgot to turn off the soap mixer on a batch of soap that was being stirred up. The result was that the mixer blended an extra portion of air bubbles into the soap, changing its density. The employee fearful for his job kept quiet about the mistake and a shipment of less dense soap went out to the stores. Its turns out that the soap bar now could float in the bath tubs, and consumers loved it and wrote to the company asking for more soap that floats.
What happens when you are trying to invent an industrial strength adhesive and you fail miserably, because your glue does not stick that strongly and can easily be peeled away? If you were inventor Spencer Silver you'd notice the other attributes of this weak glue, that it left no residue on a surface, that an object with this glue could be repositioned, and that when attached to piece of paper made the perfect removable bookmark for your book of hymns. Spencer went ahead and invented Post-it Notes.