Good Riddles

Question: When you fall in me your as happy as could be, but you fall into depression when you lose me.

What am I?

Question: How many people do you need to have the odds be in favor (at least 50% chance) of two people having the same birthday?

Question: I am a digit, but two of the ten.
Two of me make a promise.

What am I?

Question: Tear one off and scratch my head. What once was red is black instead. What am I?

Question: A father goes to prison and the mother will have to sell her hotel, but their young daughter is happy.

How can these parents tolerate such ingratitude and what put them in this situation?