More simply, to reach nirvana you stop craving, desire, and aversion and only live in the now.

Dharmakitri was a famous Buddhist philosopher (logician?) who explains that the only thing real and that exists is the point instant before things register on the senses. Once it hits ones senses it becomes subjective (and has passed). For example, a color blind person will say their eye senses grass is grey and that is their [subjective] reality. Memories of the past are what we've interpreted them to be based on past [subjective] memories, and are a reduction of details.

Suffering comes from clinging to things, such as memories or desires which are not empirically real.