When two people are in love, they tend to show only the best aspects of their nature and character to each other in order to project a good impression of themselves. Love is said to be blind and hence people in love tend to become completely oblivious of the darker side of each others natures.
In practice, each will try to highlight his or her sterling qualities to the other, and being so engrossed in love, they tend to accept each other at "face value" only. Each lover will not disclose the darker side of his or her nature for fear of losing the other. Any personal shortcomings are discreetly swept under the carpet, so to speak, so as not to jeopardize their chances of winning each other. People in love also tend to ignore their partners faults thinking that they will be able to correct them after marriage, or that they can live with these faults, that "love will conquer all."
However, after marriage, as the initial romantic mood wears off, the true nature of each others character will be revealed. Then, much to the disappointment of both parties, the proverbial veil that had so far been concealing the innermost feelings of each partner is removed to expose the true nature of both partners. It is then that disillusion sets in.