Players tend to have really inconvenient timing

Sometimes it's realistic, other times I just don't get it. Just passed the 2016 January transfer window with Barcelona by a day, when Adriano pops up to tell me he wants to leave. I say 'At the End of the season'. He says 'I can't wait that long'.......YOU'VE JUST HAD A MONTH TO TELL ME THIS!

Also, as I tend to have a first team match squad and I stick to it, it means a lot of the backup players don't play much, and I tend to have a fairly high turnover of cheap backups(at least until youth players progress). They also seem to get annoyed by late april.....couldn't they at least keep their discontent private for another month and not try to derail the clubs efforts?

I find more with injuries. Players tend to get injured in training more often right after the spring transfer window, in February and for the rest of season.