Dangers and threats, losing an advantage, increased pressure and ticking clocks, loss of control, ego-related conflict

This entry is about a character who has to stay behind while others move forward, and it covers both voluntary and involuntary scenarios. For information from the viewpoint of the people moving on, see HAVING TO LEAVE SOMEONE BEHIND.

Missing a family vacation to deal with an emergency plumbing issue
The character getting sick and missing out on a holiday get together 
Getting injured on a hike and being left behind while others go for help
A spouse taking a job in a different city and the character staying behind to sell the family home 
A character having to work during the biggest event of the year (a party, gala, concert etc.)
Missing an overseas trip to care for a sick, elderly parent
A student behind held back in school
Someone not being accepted to college while all of their friends are
The character watching their friends join an elite group that he or she can't be part of
Being the only person in a group of friends to not make a coveted sports team

Having to be self-sufficient in situations they are unfamiliar with
Dealing with boredom due to circumstantial limits
Losing money that was spent on the missed event
Friction arising in a long-distance relationship
Being bedridden or confined to the house and going stir-crazy
Missing the friends or family who left
The character being consumed with self-pity
The character haunting social media to catch a glimpse of what they're missing
Having to communicate via phone or text messaging
Learning to do activities solo (foraging, cooking, hunting, security checks, etc.)
Not knowing when others will return and so being unable to make plans
Jumping at every sound, thinking it's a loved one coming home
Having to find ways to stay busy to avoid worrying