Did you ever typo a character in your code and didn't notice, causing a fast compile or runtime error, then promptly fixed it? If it had compiled and ran with n

Did you ever typo a character in your code and didn't notice, causing a fast compile or runtime error, then promptly fixed it? If it had compiled and ran with no visible symptoms, would you ever catch that typo? That's the level of gotcha in rolling your own crypto.