Just like Bill Gates has said in a detailed interview> The first key of his success was luck, being at the right place at the right time. However, he was not the only one and not everyone who was in the same position succeeded. There is a level of intelligence, vision & drive required. The cards to do have to line up right but some of them require the person's effort.
People are definitely being generous with the word 'luck' here. Warren Buffett's "luck" consists of identifying the right investment principles (Graham's) and modifying them to include the value of great management and other intangible assets.