"Pure luck" means that something happens or is achieved entirely by chance or fortune, with no influence from a person's actions or abilities. Full definition
The other 30 % of couples who experience an increase in satisfaction in their relationship accomplish that through specific conscious efforts; it isn't by pure luck. (marriagehealers.com)
Given the large number of market gurus that now exist, the laws of statistics dictate that some of them must beat the market, out of pure luck if nothing else. (invest-faq.com)
While all divisions showed growth, it was really just pure luck. (canadianbusiness.com)