I've written 7 compilers. If you don't know you're writing a compiler from the beginning and you've never written before, it is basically guaranteed to be a hot mess in the end, unless you accidentally make exactly the right call at every one of a dozen critical steps. It's extremely unlikely to just stumble on all the good architectural ideas from a field that is 70+ years old without any planning.

Granted, if you've got a really simple language then maybe there's an upper bound on how bad it can be. But in practice people tend to also want to grow the language as they go.

Don't get me wrong; there's a lot than can wrong if you over-engineer the compiler from the beginning, including ending up with a hot mess anyway.

BTW if you can't write down, even in three sentences, the requirements for said compiler from the beginning, congratulations, you have no idea what you are doing.