Causes & Conditions
There are layers of causes and conditions for whether we experience suffering or happiness (or anything else).
Causes
The "ultimate" cause is whether awareness is identified exclusively with the small self (suffering) or has awakened to its own nature (happiness).
Another and related cause is how we relate to the inner/outer situation. Do we relate to them with gratitude and appreciation (happiness) or with resistance (suffering)? This is also tied to the habitual emotional/cognitive patterns of the small self.
Conditions
The conditions for our happiness and suffering is the inner/outer situation the small self finds itself in. These can trigger one or the other, especially as long as awareness has not yet fully awakened to its own nature, and/or allowed the patterns of the small self to reorient.