I believe in the probability associated with large numbers. Given the size of the universe and the large number of galaxies and worlds, anything that has happened once, intelligent life, has likely happened more than once. At the same time, given the large latency of the universe for travel or communication, the likelihood of us ever encountering other intelligent lifeforms is minuscule and getting smaller with time. However, the likelihood is not yet zero.
The idea of extraterrestrial intelligent life is not something that would cause me to lose sleep or spend time pursuing. There are closer resolutions to seek.