[bluGill]

The impossible part is time. You can make a car from ore that you dig yourself - if someone provides you food and shelter you could finish this task in 30 years or so. You could even make the atoms in a super collider given enough time (well energy is probably the limit).

But we need vaccines today. That means we are limited to what can be manufactured today by existing processes and factories. If you need a round iron part accurate to .001 inch (or similar metric) I know plenty of machinists. Need it more accurate and you have eliminated a large part of that supply chain, but I can still get you to .0001 inches, more than that is hard to find anyone who can handle (possibly impossible - temperature becomes a factor).