You ask AI to build a feature.

It writes the code. The tests pass. You click through the app.

Everything works.

Then someone asks:

“Why did you build it this way?”

And you open the AI chat again.

That’s a warning worth paying attention to.

Working code is only the beginning

Imagine AI builds your payment webhook.

A successful payment arrives. The customer gets access. Perfect.

But what happens when:

  • The same event arrives twice?
  • The database fails halfway through?
  • Events arrive in a different order?

The happy path can work while important failure cases remain broken.

You need enough understanding to recognize the difference.

The cost appears later

Code you don’t understand becomes harder to change.

A small feature request turns into another prompt. That change breaks something else. You paste the error back into the chat.

Soon, you’re accepting fixes without knowing what they affect.

Every change becomes harder to judge.

AI can still help you debug. But you need a way to decide whether its answer makes sense.

Try these three checks before merging

1. Explain the logic

Describe what the code does in plain language.

Where does the data come from? What changes? What happens if a step fails?

If you get stuck, investigate that part.

2. Change one requirement

Suppose a customer now has two subscriptions instead of one.

Can you identify which parts need to change?

You don’t need to remember every line. You should understand where the behavior lives.

3. Test a failure

Try a duplicate request, an expired token, or a failed database write.

Check whether the result matches what you expected.

A passing demo shows that one path works. Failure tests help reveal what you missed.

Use AI to strengthen your understanding

After generating a feature, ask:

“Explain the assumptions in this code, identify likely failure cases, and show me how to verify them.”

Then check those answers against the code, documentation, and actual behavior.

Treat the explanation as something to investigate, too.

You don’t have to write every line yourself.

You do need enough understanding to maintain what you ship.

If your AI assistant disappeared tomorrow, could you maintain the code you shipped today?