If you are dating someone on Facebook, this could be an ex you can leave alone or someone you admire, chances are you will be on their Facebook profile a lot. Or because you visit their profile so often, you always see their content in your feed.
Liked the photo by mistake on Instagram? Blocking is a solution
If you like it and don't like it fast enough, and they don't see it, blocking them doesn't make a difference. If they end up seeing it, then blocking them won't change anything – you've just blocked them for no reason. Just make sure you didn't like it quickly, and hopefully they won't see it
When you're on someone's profile and following them, or you might see their posts in your feed, it's inevitable to accidentally like one of their posts. This can be embarrassing, especially if you're way down on their profile and you accidentally like something from weeks ago.
To save yourself the embarrassment, you dislike the post in the hope that they won't find out. If you're worried about whether they'll be able to tell you liked their post, it depends.
