Note the contradiction indicated by the underlined words in the following verses:
• Gn29-18 And Jacob loved Rachel; and said, I will serve you seven years for Rachel your younger daughter.
• Gn29-23 And it came to pass in the evening, that he took Leah his daughter, and brought her to him; and he went in to her.
• Gn29-25 And it came to pass, that in the morning, behold, it was Leah; and he said to Laban, What is this that you have done to me? did not I serve with you for Rachel? why then have you deceived me?

We see the contradiction---Was Jacob double crossed by day or night?

Rashi resolves this by distinguishing two stages in the marriage: Laban gave Leah to Jacob for the wedding night. But Jacob and Rachel had personal [flirting] signs and Rachel gave these to Leah. So Jacob only fully became aware at morning that Leah was really Leah.

This Rashi has been interpreted to mean that
• Jacob and Rachel had little contact during the 7 years!
• Jacob had no memory of the women he was in love with!
• Jacob needed special signs to remind him who he was with
• Jacob did not know who he was with on his wedding night!
Remarkable! Even the lowest rif-rafs recognize who they are with on a wedding night.

I think a more palatable approach to this Rashi is the following: Traditionally men are in interested in physical characteristics while women are interested in the person. The Bible explicitly states that Jacob loved Rachel because of her figure and good looks (No mention of personality!). As is well known men and women can flirt with each other by glances and smiles. Rachel quickly found out what Jacob liked and taught Leah how to flirt with him. Laban told Jacob at the beginning of the 7 years that he couldn't marry the younger daughter before the older daughter. Jacob was at first relunctant But when Leah started flirting with him the way he liked he decided to marry Leah. However after the wedding night Leah had what she wanted and had no reason to placate Jacob. She started acting herself. It was only at this point that Jacob realized he was double-crossed and not getting the physical flirtations he wanted from a wife. Laban simply reminded him of the deal they had made seven years ago but offered him Rachel also.

Sermonic points: The above approach to Rashi makes sense. It also has relevance. It is well known that patriarchal stories create role models for the Jewish people. No Jew really worries about being double crossed in whom he marries. But it is relevant to religious men to be aware that women play such games with them--Rachels will frequently help fellow women like Leah to catch men. Women think it silly that men are interested in physical attributes and not in personality. So this incident as interpreted above has extreme relevance to us.