Professional programmers are not always synonymous with computer scientists, as programming ability is not guaranteed with a computer science degree. Writing large, correct programs is a difficult task that requires managing complexity effectively. The best programmers can anticipate failures and design software that is easier to test. Amateurs may be confident in the correctness of their programs, while professionals acknowledge the likelihood of bugs and have strategies in place for debugging. Successful programmers are not just “smart and get things done,” but also excel at writing large, correct programs with minimal probability of failure. The complexity of software increases exponentially with size, making effective organization essential.
https://www.johndcook.com/blog/2008/09/19/writes-large-correct-programs/