Source of agony

Today, while I drink coffee, I thought that what can be the most common source of agony in life. Probably I know very likely answer - ego unmatched with ability. Everybody have ego or self-esteem either strong or weak.

Among two cases, weak ego with high ability is kind of better. Although it still gives strong sense of insecurity and suffering, it naturally disappears as one's ability shines out in reality. 

Strong ego with low ability is truly a tragedy. I see this case few times in recent years. This case likely destine to be doomed as it is very much self-destructive in many ways. This is truly the source of agony, but cannot be resolved. It is lamentable that this is more common in higher educations than any other areas. Seeing this kind of people gives me feeling of watching a fish walking toward a dessert.