But this will never be an issue in the real world
  - Also Random_Rockstar_Dev_254

I see this a lot too. Which I think I have a good analogy: judging a program by its output is like judging a math proof by its last line. But math proofs are really hard and annoying because you can divide by x somewhere and then have to contend with the fact that x cannot be 0 or else you have to divide by 0, making your proof invalid. The proof is only valid in its entirety. I see programs in the same way. But this is exactly why Test Driven Development is so naive. You can't just write tests to check your correctness, it only works under the assumption that you can predict all possible classes of data that will be processed and in which way. Currently and in the future. The experience of a senior should certainly make TDD far more effective, but I'd say a graybeard is one who knows the limitations and is able to write code that is efficient, can per-emptively address future tests, and writes in such a way that the code can be easily modified and adapted for the future changes.

If I've learned anything in my history of coding it is that where the program ends up is never where I expect it to. My experience makes me better at predicting that differential, but to be honest, given a big enough project you are never really going to be able to predict the end state. Things change that are out of your control.

I'd also argue that this is why it is so important to write documentation and comments while coding. It'll help you later on and anyone that is onboarding (small cost to document, but many people reap the benefits). I don't want a junior coming in and completing a task fast, but I want them to come in and learn the codebase and how to adapt it for the task. Sure, it isn't as fast, but juniors are an investment anyways. I think we have to be honest that no matter what we do we are either investing or taking debt, both of which compound. But I think the problem is that interest is hard to observe and debt is less observable than the direct cost seen in an investment. Maybe a real Sr Dev is the one who is more aware of these trade-offs?