Everyone agrees redundancy matters right up until they look at the bill, and then it becomes "do we really need two of everything?" The honest answer is: not two of everything, but two of the things whose failure takes you down, and knowing which those are is the whole skill. Redundancy done thoughtfully is what turns an inevitable component failure into a non-event nobody notices. Done thoughtlessly it's just doubled cost and false confidence. Let me break down how to think about it.
The core idea: no single thing should be able to take you down
Redundancy is really about eliminating single points of failure, any one component whose death takes the whole system with it. Hardware fails. Links go down. Devices die. That's not a maybe, it's a when. So the question isn't whether components will fail, it's whether one component failing takes everything down or whether the system shrugs and keeps going. Redundancy is having a backup path or backup component ready so a failure is survivable instead of fatal.
The mental exercise that matters: walk your setup and ask, for each critical piece, "if this dies right now, what happens?" Every place where the answer is "everything stops" is a single point of failure, and those are exactly what redundancy targets. You don't blanket everything, you find the fatal chokepoints and remove them.
Redundancy has to be designed in, not sprinkled on
Here's what people get wrong. You can't reliably bolt redundancy onto a system that was built around single points of failure, it has to be part of the topology from the start, or a deliberate redesign later. If your whole network hangs off one device, "adding redundancy" isn't adding a spare, it's rethinking the structure so there are genuinely independent paths. Redundancy is a property of how the thing is shaped, not a feature you install.
And the independence has to be real, which is the subtle part. Two paths that both depend on the same underlying thing aren't redundant, they're one path wearing two coats. Two internet links from the same provider that share the same physical route into your building will both die when that route gets cut. Two servers in the same rack both go down when the rack loses power. Real redundancy means the backup fails independently of the primary, different provider, different path, different power, different failure domain. Fake redundancy is the kind that makes you feel safe until the shared dependency you forgot about takes both halves out at once.
Redundancy is not the same as failover, and this trips people up
Having a backup component is only half of it. The other half is: when the primary fails, does traffic actually move to the backup, automatically and fast, or does it require someone to notice and intervene? A spare that sits there while the primary is down,
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