The there is the problem of bugs introduced by the code which checks for errors and/or bugs, ad infinitum... Even the simplist program assumes the compiler has no bugs. The compiler assumes that the ALU in the CPU has no bugs. The ALU and the memory bus partity logic assumes that the logic gates have no bugs. The logic gates assume the transistors are only two state. The the two state level assumes the engineer didn't use english units when he should have used metric units. :) (except voltages is the same in both units, so an anology can go only so far - which is another logical inconsistancy!)
JLK