In my 12 year professional career and 10 years of programming before that, I can't count how many times I thought something was an afternoon of programming and I was terribly terribly wrong.
Generally good advice to be conscious about taking dependencies, but it's also worth sanity checking that something is really "an afternoon of programming."
Agreed. One has to learn to be realistic, and account for time spent thinking, debugging and testing when coding from scratch. left-pad is an afternoon project. SQLite connector may be a week project. Full JSON parser? Let's book a month to be safe.
Generally good advice to be conscious about taking dependencies, but it's also worth sanity checking that something is really "an afternoon of programming."