Most successes are unhappy. That's why they are successes - they have to reassure themselves about themselves by achieving something that the world will notice.
Physical comforts cannot subdue mental suffering, and if we look closely, we can see that those who have many possessions are not necessarily happy. In fact, being wealthy often brings even more anxiety.
Now this, monks, is the noble truth of suffering: birth is suffering, aging is suffering, illness is suffering, death is suffering; union with what is displeasing is suffering; seperation from what is pleasing is suffering... in brief, the five aggregates subject to clinging are suffering.
If there is suffering, then it's best to accept it, because it won't go away just because you pretend it's not there. If there is joy, then it's best to accept that too, even though you're afraid it might end one day.