Reading code is the skill nobody teaches

Ask a new engineer to build a to-do app and they are fine. Drop them into four hundred thousand lines of someone else’s code and ask why an invoice is off by a cent, and the difficulty is of a different kind entirely. The second task is the job.

How we teach it

• Start from a symptom, not a file. Reproduce before you read.
• Follow the data, not the call graph — most bugs are a value being wrong somewhere specific.
• Use version history as documentation; the commit that introduced a line often explains it better than a comment.
• Write down what you expected before you look. Being wrong in writing is how the skill develops.

Apprentices spend their first fortnight reading rather than writing, on a codebase none of us wrote. It is uncomfortable and it is the highest-leverage two weeks of the programme. AI assistants have made this more important rather than less: a model will happily explain code that does not do what it says, and knowing the difference is the whole job.