A complication on a wristwatch is anything other than telling time. Phases of the moon? Tides? Calendars? Complications. They make the innards more complex and fragile and difficult to build and repair. Complexity is the inherent difficulty in building the thing.

Together, what that's saying is that sometimes the minimal baseline complexity is going to be pretty high. If you're making a library to support all of HTTP/2, it's going to have lots of codepaths, and that's unavoidable. It's a complex problem requiring a complex solution. But consider SMTP, the "simple" mail transfer protocol. The protocol itself is stupidly simple. I can use — and have used — telnet to port 25 to send email. But because the protocol is so simple, implementing it is extremely complicated. Were the protocol a little more complex, the implementations could be vastly simpler.

Or perhaps more simply, if you're writing a textual protocol, define it as using UTF-8 encoding and move on. UTF-8 is more complex than simpler encodings like ASCII. Allowing your clients and servers to decide that they'd rather support something goofy, like Shift JIS or UTF-16, just makes everything vastly more complicated. Accept that the complexity of UTF-8 is inherent and sufficient, pay the cost, and then let all of your consumers be much simpler.