It’s only natural that...
This phrase emphasizes that something is self-evident or natural; it is used in formal contexts.
Examples
彼は経験豊富なプロでなくてなんであろう。
It's only natural that he is an experienced professional.
成功したのは努力の結果でなくてなんであろう。
It's only natural that his success is a result of his efforts.
これだけの出来事が起きれば、心配でなくてなんであろう。
It's only natural to be worried when so many things happen.
Quick check
成功したのは努力の結果___。