Why do marriages fail?

Why do marriages fail, after all marriages are made in heaven. People are meant to be, made for each other and all those decorative one liners.. In real life most of these one liners are more of a curse. Spouses want to find that heaven and douse it with fire. They want to find that astrologer who told their parents that this couple was made for each other and stab him a hundred times.
So why do marriages fail?
Every person thinks he knows what he wants in a spouse. Most often than not what he thinks he wants is not what he really needs. This is step 1. When he finds a spouse he feels that what he wanted and what he got are not in sync. He either adjusts to what he got and leads a happy adjustment life or remains adamant on his needs and tries to change the spouse. This leads to discord and an unhappy life or broken marriage. This is step 2.
Some people enter the institution of marriage not knowing what they want, completely clueless. After they are tied down they start to understand what they need and start evaluating the spouse against those needs. Surprise!! You married the wrong person. This is step 3.
There are indeed very few happy marriages and in such marriages what they need and what they think they need and what they get are all in sync for both partners. What are the chances for this? Very very low. The rest of the marriages that survive are adjustments. Some honest adjustments lead to happy marriages. Spouses give less weightage to their wishes and whims. They, again both partners try to see the bright side of things and try to blend into what they get. The last group is the most pathetic. They stick to their wish list and make a mess out of life. Either they end up sticking to each other due to social pressures or take the bold step of divorce.
Alas!! Marriages are made in heaven but the people getting married are mere mortals :-)