A blog post is one copy of your writing on a server. If you change your mind, you can update it (or remove it).
Email newsletters are different; more dangerous.
When you click "publish" thousands of copies are generated and sent to individual inboxes. Once you've sent an email, people can keep a copy of it in their archive, forever. You can't take it back.
Podcast episodes are like this too: once you publish an episode to your feed, the MP3 can (theoretically) be downloaded onto thousands of devices. Even if I upload a new MP3 to the feed, it's possible people have kept the old one.
When you tweet, there's technically only one copy. But if someone screenshots your tweet, they can distribute it: people can make copies, and it can live forever.
A photo I take on my phone is just for me until I publish it online, and then it can be taken by others and duplicated so many times that it never goes away.
And, going back to my first example, I suppose that even a single version of a blog post can be copied and archived on Wayback Machine.
Publishing stuff on the internet is weird.
On one hand, I like creating, expressing ideas, and sharing stories. On the other hand, it's weird to think of all these digital copies of stuff I've made just floating around... forever?
You can delete stuff, but it might never be truly gone.