If you want to learn every lesson a package manager author has learned in the last twenty years by way of counterexample, use pip.
Global dependencies by default (fixed by venvs). Shipping precompiled binaries that are not portable across platforms or python versions (kinda fixed by wheels, I forget the PEP number). No lock files with checksum verification by default (kinda fixed by requirements.txt with require hashes, but not really). Also, there's a bunch of weird sh*t that can happen if the pip version and python version disagree due setup tools.
It's got a great interface for installing stuff. But the likelihood that what it installs breaks something on your machine is pretty high the longer you use it.
Edit: the real, fundamental problem with pip is that it can't be saved. Too many dockerfiles and server provisioning scripts are relying on it - it's interface, semantics, CLI output, etc. It's not 100% broken, which is why it's still useful. But any true fix has to be done by creating a separate tool.
