There are a lot of things you can potentially accomplish in life. Some of these are far more of interest to the general public than others. I think, however, that just because the general public is more interest in them does not make them more important to you.
What makes this writing prompt fun is that there are five siblings involved, four of whom are known to be accomplishing things that the general public would find amazing while the fifth siblings, the main character, is implied to not be doing anything so generally considered amazing and yet, it is entirely possible that the other four envy their middle sibling.
It leaves the potential gender of the character open as well as those of two of the siblings. One sibling, the oldest brother, and potentially oldest child, though if both girls the twins could be older, is a military genius. I wonder if he is good at stopping wars very quickly with the least amount of bloodshed possible.
The youngest girl, and potentially youngest overall unless the twins are both boys and younger, is a scientific genius who has cured three types of cancer. That’s something that will certainly bring a lot of healing to the world.
Then there are the twins. It is not mentioned if they are identical or fraternal, but they share an interest in space and terraforming. This could potentially be a blessing if space or resources runs out and a new home is required or an additional one is. I wonder if this is something they see as being needful soon or just a long term goal.
Finally there is the main character, gender and age unknown, though most likely somewhere in the middle. No “amazing” accomplishments are listed, only the fact that they are their mom’s favorite. I wonder if dad is still in the picture and if he is, does he also have a favorite. How do the other four feel about the MC being mom’s favorite?
This one potentially takes a lot of know how, but it could also be a lot of fun, especially to see how all these different siblings interact with each other. What do you think would be the greatest challenge for writing a story from this prompt?