They think it is easy to do when it is not. They think marriage is a smooth sailing ride when it is not. It is totally worth it in the end. Maybe hard but that why your partner is there to help. If you can't do it than don't do it.
Commitment is important in marriage, of course, but it does not always mean committing to life together forever. It can mean honoring the union and being loyal to it while one is in it. It can mean acting honorably when one or both people feel that things have changed and divorce is inevitable.
In a day and age where it is perfectly acceptable to just live with someone, and not necessarily feel pressured to marry, there's no reason to marry unless you are truly devoted to the other person. Unconditional love seems to be a rare commodity these days. If you are not absolutely in love with the person you are marrying than don't. People shouldn't get married just or kids, or because families think they should. All of this said, it's up to individual couples to decide what that commitment means. For one couple monogamy might be paramount, and for others, and open marriage is perfectly acceptable, as long as at the end of the day, they come back together with their one and only.