I think the things that trip people up are:

1. People expect k8s to be an opinionated platform and it's very happy to let you make a mess

2. People think k8s is supposed to be a cross platform portability layer and ... it maybe can be if you're very careful, but it's mostly not that

3. People compare k8s/cloud/etc to some monolithic application with admin permissions to everything and they compare that to the "difficulty" of dealing with RBAC/IAM/networking/secrets management

4. People don't realize how much more complicated vanilla Linux tooling and how much more accidental complexity is involved