The saying easy as pie has always struck me as being not all that accurate. Pie can be hard, stubborn, finicky - and that’s lattices aside. Crusts can crumble, or worse, become tough and chewy, the opposite of your grandmother's flaky version you were trying for.
To make things (actually) easy, the Culinary Institute of America offers tips from their pastry chefs on how to make the perfect crust. They explain the science behind why colder ingredients are better when you’re making a pie crust, and how you should actually freeze everything for a spell before starting in. They even give you a ratio, too, of flour to fat to liquid. You still may not be able to make one with your eyes closed, but hopefully from now on, pie crusts can be a bit more foolproof.
Pie-Making 101: How I Overcame My Fear Of Crumbling Crust from NPR