Pastry is generally dry, delicate, and flaky. The delicacy and flakiness of a pastry is determined by how much the dough is mixed, how thin the dough is, how much fat is involved, and the melting properties of the fat. A pie crust, for instance, is delicate due to the relatively low amount of mixing (and hence, low gluten production), and is flaky due to the high fat to flour ratio. A croissant dough, unlike a pie crust, will endure a high amount of mixing (thus more gluten) but the dough is rolled into very thin layers between a large amount of fat.
One of the main goals of pastry dough preparation is to avoid combining the fat and the other ingredients. The fat should be distributed in the other ingredients while remaining unique from them; in a pie crust this is achieved by using a pastry blender to cut the fat into small chunks, which "float" in the rest of the ingredients, while in a croissant this is achieved by mixing the dough separately, folding the dough over the fat, then rolling and folding the dough over itself a number of times to produce distinct layers of dough and fat.