Most Helpful Guy
There's lots of reasons. For some it is depression, for others it is deeper, like realizing that free will doesn't exist, or that the probability of what we call reality actually being real is something like 1 in 3 billion. There are lots of very deep reasons to lose interest in life, I could write a couple thousand pages about it, and still not cover them all.
Most Helpful Girl
Well, depression, maybe. Or maybe the thought about why we live in general. Once you think about that, sometimes, its like, why bother?