Every time I make pasta (which is all the time), there's a good chance I have a mug hanging out on the counter near the pot. Not because I'm drinking coffee with dinner (although I wouldn't put it past my coffee-dependent self), but because it's standing by to be filled with boiling water before I drain the pasta in the sink.
Why? Because that pasta water is the secret ingredient that takes sauce from dry to silky, and from incomplete to cohesive. Once your pasta is al dente, the water that remains is starchy and salty (that is, if you added enough salt before adding the pasta — it should taste like the sea!), and the liquid clings to the pasta and aids in creating a creamy sauce, no cream necessary. If you're a seasoned Italian cook, you know this for sure — it's one of the oldest tricks in the book, and it's even one of Giada De Laurentiis's pasta tips from her grandfather. Personally, I learned it from my mom, and now it's a second-nature step when I make any number of pasta dishes, like carbonara, amatriciana, and cacio e pepe.