Yes. So many developers think, I string together some APIs into something that looks like an app, I've done something. Forgetting those libraries are designed/tested to work only on whatever subset of the problem space they were used for previously. They probably don't handle your case; they don't have explicit capacity promises; they don't work together (don't respect each others backpressure signals, don't understand each others error spaces etc).

I read open source, then extract the bits of IP I think was useful. Often rewriting it to fit my case. Its useful source, but as an example to help me write my app.

{ Please don't use Linux as a strawman (You rewrote Linux?! I don't believe it!) That's the single largest, most successful (along with maybe 5 others) open source project. But absolutely not representative of the 1M other projects out there. }