Just an idea might not be enough to write a full post. It might feel like it, but run short after few sentences. Or it could be I don't have enough knowledge yet to write about the topic.
Following rules and best practices can be overdone. For example it's good to write shorter sentences. But making every sentence as short as possible makes the text sound like a telegram STOP
Sometimes it's better to just write the thing down without worrying about the correct form. Of course when writing these quick posts there is no editing phase, but in general it's better to leave that for later.
There is always something better to do instead of writing. There won't be better moment later. So better to get it done with as soon as possible. Writing tired and in a hurry without a good topic is worse than just writing without a good topic.
Using different tones of voice can greatly alter how the text "sounds" like. Writing about the same topic in different tones can give completely new perspectives.
There is always something to write about.