Testing a bridge: put a 1000kg on it and you can infer that 500kg will also work.
If testing a bridge were like software: you would put the 1000kg on it. Repaint the 1000kg barrel red instead of green. And the bridge would fall down.
Most mechanical systems now heavily rely on software to handle control. Engineering of any kind is tough: software, mechanical, chemical or (insert favorite discipline here). I am not really a fan when one discipline beats up on another discipline for being "easy." Anybody who says building software is just coding can walk in my shoes for a few days.
Or it might hold up for every multiple of 1 kg from 0 to 10000 kg, but collapse on 133.7 kg because of some horrible floating-point detail.
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