Scientists who research this stuff have determined it's mostly luck and opportunity. Here is the conclusion of a Scientific American article titled The Role of Luck in Life Success Is Far Greater Than We Realized

The results of this elucidating simulation, which dovetail with a growing number of studies based on real-world data, strongly suggest that luck and opportunity play an underappreciated role in determining the final level of individual success. As the researchers point out, since rewards and resources are usually given to those who are already highly rewarded, this often causes a lack of opportunities for those who are most talented (i.e., have the greatest potential to actually benefit from the resources), and it doesn't take into account the important role of luck, which can emerge spontaneously throughout the creative process. The researchers argue that the following factors are all important in giving people more chances of success: a stimulating environment rich in opportunities, a good education, intensive training, and an efficient strategy for the distribution of funds and resources. They argue that at the macro-level of analysis, any policy that can influence these factors will result in greater collective progress and innovation for society (not to mention immense self-actualization of any particular individual).

UBI will smooth the distribution of wealth out a little. There will still be lazy people and ambitious people.