The reason to try a new approach to things is because you have demonstrated proof that existing approaches are not working.

let's unpack:

1. what counts as proof?

2. what counts as failure?

3. not working for whom?

4. not working towards what end?

what counts as proof? and what counts as failure?

in order to answer this one needs to understand a thing well enough to know what success looks like and to know what failure modes exist.

A thing can fail by succumbing to a known failure mode, or failing in a new way. New failure modes commonly emerge from new contexts. Or they may be due to new developments in an existing context.

proof of failure means you have observed (rather than concluded via hearsay or via abstract reasoning) failure in a known mode or new mode. in order to obtain this proof, a relatively close distance or even insider perspective is usually necessary.

failure modes are specific to the thing being examined but there are some very common patterns. here's a couple of the most common patterns: