If you made something yourself, the more complex it becomes, the more likely it is to fail. Take a space rocket compared with a bycicle.
You're not defining "failure" properly.
Even though a bicycle is more reliable at bicycling than a rocket is at rocketing,
a bicycle is less reliable at rocketing than is a rocket.
In other words, a bicycle is successful in its niche of low speed ground transportation,
& a rocket is successful in its niche of transporting satellites & astronauts into space.
Complexity is necessary for rocketry.
Now look how complex one part of the human system is, say the immune system, or the eye, the respiratory system, a cell, all complex, all have to work together and keep working together. All through blind chance on matter and all needing some parameters to make it all work, such as natural selection.
Here's your recurring error....."chance" is not blind.
The fitness function of a stochastic system is what 'selects' the winners.
It is not pure chance.