I heard a great vort last night in the name of Rav Yankele Galinsky from Bnei Brak:
It is brought down in the midrash (which Rashi quotes) that Leah was supposed to have another son. She knew that Rachel would be distressed that she would not even have as many sons as the maids (she would then only have 1 son to their 2 each) so she davened that Hashem should give the son to rachel. Rachel was subsequently blessed with a son to be named Yosef and leah's pregnancy was changed to a girl named Dina.
Not only was she so righteous as to give up a son and tribe of Israel to save the honor of her sister, but then Dina went ahead and married Shchem. After all that Leah ends up with a son-in-law like Shchem? Where is justice in the world?
Rav Galinsky explained that everybody gets what is coming to them. Sometimes you need patience, as things do not happen right away. Leah gave up Yosef to Rachel, but look how it happened. Leah had Dina who married Shchem. Together they had a daughter named Osnat. They sent Osnat down to Egypt who eventually married Yosef, the ruler of Egypt under Par'oh. Together they had 2 sons, Menashe and Ephrayim, who were given by Ya'akov the status of 2 Tribes.
She did a righteous kindness and gave up one tribe, but was paid back by eventually having 2 tribes in that one's place. God always pays back what's coming to you. Sometimes you just have to wait, and Hashem makes it worthwhile.
After hearing this vort, I was thinking about it and realized that really Leah owed everything to the kindness of Rachel. Rachel had been sensitive to Leah's feelings and allowed her to marry Ya'akov in her place. Leah was returning the favor, so to speak. One could easily say from these messages that it is more important to be sensitive to another's feelings and needs than to deman what is coming to you. Don't worry about Gods cheshbonot (accounting practices). You do the right thing and you will get what you deserve and more.