> Every couple of months or so I get really annoyed when I see that someone built something I already thought of but dismissed as not good enough of an idea/problem or as a waste of time.Don’t pay too much attention to what other people have done. Most people with an idea will never see it to completion [1]. And even if there are large companies already in a space there are very few winner-take-all markets. Even companies like Apple have small competitors (e.g., Framework).
Also, not every idea needs to be original. Most companies copy or improve on others’ ideas. Google, Microsoft, Oracle, Apple, and Amazon might have pioneered new markets once they were already big, but they certainly started out as iterative improvements (or better marketing) over existing products.
[1] in fact, one of the best things you can do is reach out to people who already tried and failed at an idea and see if you can learn about why. Or if they are still in business, reach out to former employees. A lot of people will be surprisingly candid with you.