Accept the things I cannot change

In every job I've had (minus high school babysitting and being a cashier at Ace Hardware), I see inefficiencies, inconsistencies, or injustices and I get passionate about fixing them.  This is probably the #1 cause of stress and frustration for me at work because most places don't like their flaws being pointed out and are resistant to change.  I'm having a moment where I want to push for changes, but I know it will be frustrating (and could very well result in a poor annual review in addition to not making any change).  I'm trying to remember that this is not my company, that it's just a job, and that I can still be good at it without bucking the status quo.  I need to master the mindset of accepting the things I cannot change if I'm ever going back into the public school system.  This is good practice.