“The problem is, if you’re not a hacker, you can’t tell who the good hackers are.”
Paul Graham
To understand Docker, go read about cgroups.
To comprehend Bitcoin, go delve into its white paper.
To learn MapReduce, go study the original authors’ work.
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To know what a code does, go read its source code.
You’re not going to get confident in a code by reading the documentations only. Go for the origin whenever you can. Reach the lowest level that you can reach. Yet, following this principle too rigorously eventually leads you to the design paradox1 situation. You’ll reach a point that you can’t rely on anything unless you a have complete understanding of every small detail. Read the code, but don’t go too far!