People have built complex bug free software without __formal__ code review. It's very rare to write complex bug free software without at least __informal__ code review, and it's luck, not skill.

Can't have a code review if you're coding solo[0], unless we are redefining the meaning of "code review" to the point of meaningless by including going over one's own code.

0. The dawn of video games had many titles with 1 person responsible for programming. This remains the case many indy games and small software apps and services. It's a skill that requires expertise and/or dedication.