If you don't know, the acronym RTFM means "Read The Friendly Manual". And this is exactly what I've done several months ago, when I've used a third party library. I've made a simple test program and everything seemed to work just fine.
This week, I've used that library for work and I've started to see some strange behaviors in my app. The output of the old test program was still correct, but the same code in a bigger application caused wrong values being shown and some crashes.
It took me hours to understand where the problem was. And, can you guess?, I found it only after reading the friendly manual carefully. It was clearly written that some returned data were references to members of a structure.
What I was trying to do was to access them after the structure was freed. The simple test program seemed to work fine just because it was too short, so the memory just freed was not overwritten by anything else.
Lesson learned: it's not enough to read the manual; you have to read it carefully. Or, if you prefer an acronym: RTFMC.
Image from xkcd licensed under the Creative Commons Attribution-NonCommercial 2.5 license.