"There's nothing new under the sun"
The blog post you linked quoted this. I'd expect most native English speakers would have heard it before, even if they wouldn't know where it was from. For example, "This new AI stuff doesn't really change anything--our business model is still the same. There's nothing new under the sun."
A potentially similar phrase is "The more things change, the more they stay the same".
"You aren't the first (and you won't be the last)"
This is an expression of sympathy, especially for a common mistake that many beginners make. For example, "You aren't the first college student to decide to stay up all night before the exam, and you won't be the last."
"Somebody already beat you to it"
Somebody has already done whatever you were going to do, especially if it means that you won't get anything from doing it second. For example, "Hey, you know that app idea you had? Looks like somebody already beat you to it."
"Ideas are cheap (execution is what matters)"
In the specific context of the linked blog post, this is similar. It means that it doesn't matter if your idea is great and original if you can't make it well, and that an unoriginal idea can be successful if the execution is great.