Is it possible to be enlightened? Within the Theravada tradition, there are four stages of enlightenment. The first stage is that of stream entry, which offers the adept a glimpse of Nibanna and the assurance that no more than seven rebirths are ahead. The next stage is that of the once-returner, which involves at most one more rebirth. The third stage is that of the non-returner, which involves no more rebirths in sensory abodes but rebirth in a pure abode. The fourth stage is that of the arahant, who will not be reborn and thus will be released from all suffering.
I once was studying with a very senior monk. I told him, I thought rather modestly, that my aim was stream entry. He agreed with me; that was his aim as well.
When I first started meditating in the Soto Zen tradition, my aim was satori. I was sure if I tried hard enough, I would attain enlightenment. However, I quickly realized that this meditation thing was a bit more complicated than I thought. I got discouraged after about a year of working on it and abandoned my practice. I came to understand in my later years that aiming for enlightenment may not only be unrealistic but counter-productive as far as keeping up with the discipline of daily meditation practice. When I started meditating again, I decided that all I really wanted to do was to improve myself: to be less distracted, to be a little wiser, and to be a little more virtuous. This motivated me to continue to meditate. Once I realized that these goals were attainable, I was able to sustain my practice and keep up the discipline of daily meditation.
In the Mahasi tradition, there is a strong message that enlightenment or some stage of it can be attained "in this very life." On retreats, especially prolonged ones, this goal at times seems possible, especially when there is an inspiring teacher who exhibits the qualities associated with being an enlightened person. However, at other times, when one encounters the chaotic, confused and obsessive mind, it seems very much out of reach. At times like these, I remind myself of the modest goals of being somewhat more focused, somewhat wiser, and somewhat more virtuous. Because meditation is demonstrably beneficial in these ways, I continue with my practice.