Hey hey hey! I have a question for you. I have seen several writers post that you should not start out writing a book you want to publish, instead you should write your first one just for practice before starting on the book you’ve always wanted to write (does that make sense?) Do you agree??? I only have one book idea that I want to write (and hopefully one day publish), but I don’t know if I should write other things beforehand if that’s what’s best...
This is a super interesting question! Definitely write the book! Write the book idea you want to write! (Also write other things too, if you need a break.)
Personally, my thoughts on the matter are that if you have ANYTHING AT ALL to write, write that. Don’t worry about getting published (like at all, like don’t even think about it, neither positively or negatively,) you can definitely publish your first novel. This attitude you’ve discovered might be considered the ‘rule’ but there are always exceptions to the rule, ( e.g JK Rowling ) However I think it’s best not to compare yourself to the greats, compare yourself to smaller indie writers, because while it is important to have aspirations, it is also important to have relatable idols too, realistic goals.
Write the book you want to write first.
Look into the How To of the publishing world afterwards (or look now if you want) but I think the main take away from that old sentiment should be, don’t write your first novel with the SOLE purpose of publishing it. Write it because ultimately you want to, you have to, you need too. Publishing is a bonus :D
I get their point about practicing writing though, you're first novel may not be your masterpiece. You will get better at writing as you go, but don't rely on that future self before you have constructed them. Write now! :D