This is why no one under the age of 35 should get married (until then, they’re usually still maturing), and only after a minimum of one year living together. Let’s face it, a 20-something couple is still rapidly changing and learning, and completely clueless about themselves and life in general.
If “a lot of work and effort” is necessary to save a marriage, I’m inclined to say that those people should not be together. Some compromise is essential, of course, but if you consider your marriage full time “work”, you’re incompatible. I believe friendship is more important than love for a couple to be happy in the very long term. Love comes naturally when you like spending time with someone, and it has little to do with the obsessive feeling of being “in love”. IMHO.