Yes, it's sunny here. It's 10 a.m. and about 35 Celsius only as the summer is almost over. And I'm at work 
Why 'stuff is'? It is not a philosophy but it is what it purports to be - a philosophical idea, especially if you interpret stuff to mean not only physical objects like stones but also forces like gravity, concepts like relativity, human constructs like law, events like birth and death. It's all stuff, and affirming its being in two simple words is a celebration of all of it, and possibly a reminder against self obsession, since there is so much more than self.