There’s a massive difference between ‘having the idea’ and elaborating that idea into a complex and rational theoretical apparatus and situating it within a philosophical problematic. Often we don’t even realise that initial idea was ‘good’ until someone does the actual philosophical work. As pascal pointed out, Augustine had something like the idea cogito, but it was Descartes who was able to use that idea to completely revolutionise philosophy and how we think about the subject.