The speed in agile should be your speed to fail - to prove an idea does not work while still cheap enough to change tact. The time to build the whole might be

The speed in agile should be your speed to fail - to prove an idea does not work while still cheap enough to change tact. The time to build the whole might be no faster or even slower - but then again you might find out that after delivering only half the 'required features' that you have done enough to meet the customer need, and stop there. Big projects rarely want to stop though until the shopping list is complete.