Moral dilemmas and temptations, failures and mistakes

Injuring someone in a car accident 
Playing a part in ending a valued relationship 
Abusing or neglecting someone in the character's care
Poor decisions causing the character to miss a once-in-a-lifetime opportunity
Making a decision that costs the character their family's life savings
Giving into temptation, with disastrous results (an affair ending the character's marriage, drug use killing their dream, etc.)
The character realizing that their parenting methods have caused irreparable damage to their child
Not being available for a friend during a crisis
Crossing moral lines to survive (in a time of war, when homeless, as a child, etc.)
Killing someone in self-defense
Missing signs of depression prior to a loved one's suicide
Not voicing suspicions about someone who, later, goes on a killing spree
Staying in a bad relationship because the character believes they deserve punishment

Having to apologize and knowing it's not enough
Needing to be truthful with family members even though it means reliving what the character did
Having to talk about the situation to officials
Being unable to focus on day-to-day tasks
Losing time at work to seek therapy
Trying to think of ways to rectify the situation or make amends
The character being especially hard on themselves, even in daily tasks
Others thinking less of the character for their actions
The character running into a person who was hurt by their actions and not knowing what to say
Having anxiety or nightmares 
Loved ones misreading the situation, believing the character is feeling sorry for themselves