You can't even make a start.

It has to work

If it fails people will be hurt, you will be sued, the financial losses will ruin you.
We are talking potential disaster here.
Regulatory authorities demand due diligence. Real disasters have happened in the past and the authorities don't want any more.

I can apply best-practice methods to ensure that the implementation is not only bug-free but also can be shown to be bug-free.

I have designed and implemented applications which are classified by the United States Food Drug Administation as life-threatening.

I have invented tools to assist in using these methods.

I have used these methods in less demanding situations simply because it was convenient to do so. You can save a lot of time and effort if you cut out the rework and retesting that ad hoc development leads to.