At the beginning of "The Lottery Ticket," Ivan Dmitritch is described as a man "who lived with his family on an income of twelve hundred a year and was very well satisfied with his lot." He is sitting peacefully after dinner, reading the paper. Not much later, the story ends with this formerly contented man reflecting miserably on his misfortune and crying savagely:

Damnation take my soul entirely! I shall go and hang myself on the first aspen-tree!

Ivan Dmitritch's situation has not changed since the beginning of the story. He has not lost anything in reality. In his imagination, however, he has won and lost a fortune—or his wife has. Even without ever getting their hands on the money, both husband and wife have spent it in their minds, quarreled over it, and been made miserable by it.

The main theme of the story, therefore, is the way in which trouble and unhappiness are primarily the product of one's own mind. This is particularly true for modern, middle-class, comfortable people like Ivan Dmitritch and his wife, Masha. Some people, of course, are sick or starving, or have other genuine troubles. The couple in the story, however, had no financial worries before they thought they had won the lottery, and the prospect of this large sum of money merely makes them anxious and hostile to one another. They have everything they need in life, and it is only their foolish and destructive thoughts that make them unhappy.

Love of money, as they say, is the root of all evil. In “The Lottery Ticket,” by Anton Chekhov, it's the prospect of winning a large sum of money that proves to be a major source of evil, generating considerable tension between an ostensibly happy husband and wife.

Before fate dangled the prospects of phenomenal riches before Ivan Dmitritch and his wife, Masha, they were an ordinary, middle-class couple leading what appears to have been a fairly contented existence. But when it seems that Masha's ticket has won the lottery, their heads are suddenly turned, and they start fantasizing about how they will spend their imminent windfall.

In doing so, however, they start to become deeply distrustful of one another. Both Ivan and Masha quickly come to believe that the other is going to be negatively changed by their sudden good luck. Ivan is worried that Masha will either abandon him or use the money to control him. As for Masha, she resents Ivan for wanting to spend what is, after all, her money. (It was her ticket that won the lottery.)

In both cases, what we can see is a prime illustration of the way that money—or in this case, the prospect of money—can corrupt the soul. What was once a contented marriage has been contaminated by mutual loathing and suspicion, and all because of a lottery win that turns out to be no such thing.

The central theme in "The Lottery Ticket" is the exploration of how money affects and corrupts those who possess it. The couple in this story imagines what they would do with the money if they should win the lottery. Up until now, the couple has lived comfortably and in relative happiness; however, their thoughts about what they would do should they become rich reveals how money affects people, even if it is just the idea of money. This is shown through their sudden dissatisfaction with the home that they previously found to be comfortable once they realize that they have not won the lottery. The couple once felt contentment with their life, and now, merely the idea of an extravagant lifestyle has made them long for more.

Anton Chekhov's short story "The Lottery Ticket" follows the brief imaginings of a married couple after they discover that the wife's lottery ticket has a matching series number to the number posted in the paper. What will determine if the wife, Masha, receives the money is if the secondary number matches as well. Rather than immediately look to see if they have the entire winning number, the couple speculates about what they would do with the money. While these daydreams start out pleasantly enough, eventually both the husband and wife start to feel a rising sense of discontent, hatred, and resentment for each other. The husband privately bemoans the fact that his wife has aged and that he could have remarried someone younger, while the wife considers how her husband will likely try to appropriate all of the winnings for himself.

Ultimately, this story deals with the theme of greed and how the desire for material possessions is ultimately what poisons us. From Chekhov's point of view, wealth is the seed of dissatisfaction, and it eventually leads to the unraveling of our gratitude for what we already possess. 

To me, the theme of this story is that it is best for people to be content with what they have and not to start dreaming of things that (they think) will be much better than what they have.

The couple in this story were relatively happy with one another.  But then they thought they had won the lottery.  Once they thought this, the husband especially began to have big dreams.  He became dissatisfied with what a moment before had been an acceptable life.

Another way you could look at it is to say that the theme is that you should not let a change in your wealth (or other circumstances) change who you are as a person.