How do you overcome it when you realize that solution you had been working on isn't original

It’s very hard to come up with a truly original product or service, and that’s perfectly fine. Instead of feeling down about it, think of the positives: somebody has already helped you validate the idea, so now there’s a ton of research that can help you: How big is the market? Who’s signing up with them? How are they finding their customers? What are they doing that’s working/not working for them? What can you do better? Is there a different niche that they’re not serving? Your idea doesn’t always have to be original. It just needs to solve a problem that someone is facing better than your competitors.

By your way of thinking, a lot of businesses exist shouldn't. Why create Lyft when there's Uber? Why create Uber when there's taxis? Why have Hinge, Bumble, CoffeeMeetsBagel etc when Tinder already exists? Why are there locally run coffee shops when there are big well known competitors like Dunkin Donuts or Starbucks? Competition is healthy and pushes people to be innovative. Monopolies are actually bad cause then you give the consumer no choice but to buy from one place and that's too much control for one entity (think big pharma and their influence on drug prices). You as a creator, just have to capture a part of the market. You know the idea is good cause someone else also thought so (and is doing it). You just got to figure out what you can do different, whether that be a pain point that a competitor hasn't addressed, better customer experience or branding. Definitely don't go chasing for the perfect idea. Execution matters infinitely more than the idea.