This QT version or that? Hunt down some weird dependency. Find that that dependency clashes with a more recent version, but you can't downgrade. Oh, oops your app depends on a quirk in glibc v x but your system only has v y so now you have to figure out how to run two different glibc's without conflicting with each other, and better not make a mistake during that installation or your system may never boot again.
Complex software can be quite a pain to build properly, more-so if you want to target multiple different architectures or operating systems.