If you design and develop for others, you will be much more disappointed. I usually design things based on my own needs and share them with the world. If no one is using it, I'm using it for myself, at least, so I'm my biggest fan.
I wouldn't say I've had too many failures, although I'm just getting started. However, I've done some testing the past few years and put out some free products out there and tweeted about them only. Then I waited and watched.
In 2015 I created a product called https://mypost.io which allows anyone to have a web page up on the Internet in seconds. It is a very simple blogging / web page creation platform that even lets people use HTML and CSS to design their pages. The test was: Will people find it useful and actually use it? I added OWA so I could see the location of where people were using it from and I've seen people as far as Russia using it.
This let me know at least I was on the right track to creating something useful. I'm sure if I had the funds to really market and advertise my products, I'd be able to push them much further, but the hope for now is that people share it if they find it useful.
While I wouldn't say that I'm monetarily successful at this moment, I did build a popular website, and was able to gain and use that traffic to drive attention towards things I'm doing.
Failure is what eventually leads to success. The reason it keeps getting better for you is because you are learning from your mistakes and constantly changing for the better. If you didn't do that, than I might be more concerned and might tell you its time to call it quits. But your perseverance, ambition, and desire for success is going to work out greatly in your favor when the time comes.