In Anton Chekov's "Gooseberries," Ivanich claims there is nothing sadder than the sight of a happy person.
Thinking upon this, after reviewing the story, I believe there are two reasons he might say this. Ivanich tells the story of his brother, a man who wanted nothing more than to have a home in the country and grow gooseberries. His dream becomes his obsession: he believes that if he can reach these goals, he will be truly happy. He works hard, marries for money, scrimps and saves, and finally gets his house with gooseberries growing outside.
When Ivanich goes to visit him, he sees what a toll life has taken on his sibling as he has scratched through his days to achieve the things he thinks will bring him satisfaction at last. The sight of his brother saddens Ivanich. Even the gooseberries his brother so adores are in reality sour and hard, but in this brother's mind, because they were his dream, they are wonderful and he cannot resist them. Ivanich thinks his brother is deluded. However, regardless of the manner in which his brother finds joy in his life, he still feels wonderful for what he has...and Ivanich does not.
When he becomes more philosophical, Ivanich seems to believe that happiness is only possible when one is unaware of the unhappiness of others. (And since there will always be the unhappy, it should be impossible for anyone to be happy.) Only by putting their heads in the sand, hiding from the sad realities of others, will people be able to maintain their joy with their circumstances.
Ivanich, now that he has taken this idea to heart, appears to believe that he is too old to find happiness and mourns the loss of his youth. He admits that once he was happy, but finds himself now discontented. It seems that he believes it is because he is aware of the sadness of others, but I don't think this is an accurate perception on his part.
Perhaps Ivanich's sense of sadness simply comes down to his own personal lack of success in finding something that he can celebrate. He says he is too old himself to struggle to become happy, and now must mourn the lost days of his youth, and look bleakly into his future with the knowledge that life for him will never be good. However, the sadness he experiences in seeing a happy person is of his own making. I doubt Ivanich can see this.
Ivanich feels that those who are happy are that way because they do not see the reality of others' lives—therefore he thinks they are delusional. The truth is probably that Ivanich is the deluded one. Despite the "blindness" others experience, life still brings them joy. Ivanich thinks he has figured out that happiness comes at the expense of others, but this is not necessarily so. However, because he believes these things, he sees only gloom for himself, and it is doubtful that he will ever know another happy day in his life. His outlook on life, and nothing more, makes it so.