This is very true. Some people can put on a metaphorical mask to cover the barrage of shit that is affecting their lives on a daily basis. They then take this mask off when they are in a solitary place a weep so the world can't see. These people are the strongest of people. The ones who will take your crap, be your shoulder to cry on and the one you always turn to. But who do they turn to when that mask comes off? Can they turn to anyone as they are perceived as 'the strong ones'.
It may come as a shock to some that this actually happens. And the sooner people realise this the better. Calling someone grumpy when you know they are having a bad time is just poking a huge bear with a stick - you are going to get your face ripped off and told to go fuck your self with a cactus!