I get what your saying, but I think your still very much underestimating how complex earth's ecosystem is (as @grant permission pointed out).

On this planet we still can't predict the weather 100%. To survive on Mars we're going to have to build and sustain a mini-earth ecosystem and "program" the weather for that ecosystem.

Food, water, waste managment, power, air...the list is long. All systems must be individually and jointly sustainable and synchronized by a computer system.

Look up the 5 levels of "autonomous driving." We are somewhere between 3 and 4. A long ways from 99%. Many experts believe we'll never get to 5. I'm not so pessimistic, but like every other system it follows on of the 80/20 rules. 80% of the work is finishing the last 20%.