If you practice diligence, you are a hard and careful worker. Do you have the diligence to read all the collected works of Henry James? Of course not. Nobody has, but a couple of his early novels won't hurt.
Here's a tip: never buy anything big, like a house or a car or a boat, without first exercising what lawyers call "due diligence" — that is, a real degree of care and attention and effort, not to mention a close reading of the small print. Diligence may help you realize the Brooklyn Bridge is not actually yours to buy, or that your potential neighbor has 112 cats living next door.