Ask HN: What are downsides of Kubernetes/containers?

I have been reading more about Kubernetes/container management and I see a lot of excitement around the technology on HN.

What I am trying to understand is the downsides of container platforms like Kubernetes:

Are they more or less resource efficient than what you had before?

Are they inefficient at using resources, but make life just so much easier that it's worth it for saving dev time?

Are there many managed solutions (aside Google cloud) or are people deploying this themselves?