Almost certainly you have a powerful ability to put together explanations when you see something happening (in the street, for instance). A huddle of people are looking up at a tree, so there's probably a cat stuck up there. A man is sitting on a shop doorstep, and he's likely to be homeless and will ask you for money. Of course we don't always get it right, and our assumptions can prove wrong. The tree observers could be council workers discussing a pruning job. The man in the doorway could be simply tying his bootlace.
However, there was no doubting the cause of a little scene I saw acted out the other morning on my way to work. Outside a nearby children's nursery, a young mum was smiling and waving through the window. I saw her first. A few paces on, I spotted her little boy inside, with the unhappiest face in the world: he clearly didn't want to be left there. As I walked on, it seemed mean and heartless of the mother to be smiling. Surely she'd be upset to see her son in such distress? Thinking more, though, she was probably doing the right thing, trying to get her little boy to see it as normal, nothing to get het up about, and this is probably a good way to hope others might behave around you when your own mood is low. Naturally, you'd like them to empathise with you, but the last thing you'd want is for them to suddenly become as low as you are. It's a fine balance, though, worth exploring when the boot's on the other foot and you're around someone else whose mood is low. The answer? Almost certainly to be yourself, and behave as normally as possible.