"The easier it is to leave a marriage, the less reason there is to invest in one."Is this to be understood that it is worthy to invest in the marriage only when it is very hard to get out of it (and we of course take the stance you don't get married with such a intention)? I truly believe that the investment in marriage should not be in any case connected, or stemming from, or related to the level of "trap" (and I don't agree in a first place with such definition of marriage). 'They had the positive incentive of love and happiness, as well as the negative incentive of strife, compelling them to invest in the marriage.'You have the positive incentive today also. And you have the negative incentive today, too. Strifes happen. They happen because two people sometimes, many times, have different views, wishes, sometimes competing ones. If you expect strifeless marriage, you expect a marriage in which one of the sides will always give up, thus avoiding a quarrel (and probably you expect it will be your partner). It is an unhealthy approach, because it disqualifies any discussion on matters where there is a disagreement. 'They do not have the negative incentive of strife forcing them to get along, because if things sour they can leave. They instead have a counter-incentive restricting their investment.'As mentioned above, two people that decide to live together in a marriage, enter the marriage with the persuasion, that they want make it work. Strifes included. Strifes should not be reason to get out of marriage. If you enter the marriage with the intention that you can leave at any time it is not comfortable, it is wrong and you should not get married. That is why before getting married, the two wnat to know whether their prospective life-partner is someone they can communicate problems with, who is willing to meet their needs, but at the same time they should ask themselves whether they are willing to meet their needs (as their partner articulates them, not as you articulate for him/her). After all, there are two questions. Theoretical one: What is the nowadays marriage based on?And practical one: Why do you want to get married? And why with this person?They are not necesarilly to be answered in the same way. Or, even if you have doubts, or you don't know the answer to the first question, you definitely must have an answer to the second question, if you want your marriage to have some chances to endure ad 120.