Loss of control, losing an advantage, ego-related conflict, duty and responsibility, miscellaneous challenges

Developing a chronic condition that leads to short-term memory loss
Sustaining a concussion that affects the memory
Experiencing a traumatic event that results in the suppression of memories
Growing older and struggling to recall past events
Getting an acute illness that temporarily affects the memory 
Taking a drug that inhibits cognitive abilities
Being slipped a medication that makes the character forget things
Not sleeping for days on end, then being unable to recall details clearly
Struggling with mental health issues that impact the character's ability to recall events correctly
A high-stress situation clouding the character's memory and recall of details

Losing credibility with others
Being pitied by others
The character's autonomy decreasing out of necessity
Getting frustrated when people claim things happened differently than the character remembers
Frequently misplacing items 
Needing help with everyday tasks, such as cooking or tying shoes, because the character has forgotten how to do them
Having to give up a favorite hobby because the character can no longer remember the rules
Not recognizing that there's a problem
The sickening feeling when the character realizes they've already asked a question or had a conversation
The character losing their train of thought mid-sentence
Forgetting a deadline or appointment
Needing to have someone else drive them around for a while
The character forgetting their name or other important personal information
Not recognizing a loved one or friend