When you look at all of Teen Mom, all the people from all the series and all the terrible, traumatic things they've all been though ...
We still think there's a good chance that Leah Messer's story is the saddest.
She was just an average high school student in West Virginia, having fun and being a teenager, when she found herself pregnant.
After a rebound hookup, no less, with a guy she'd just met. Messer's fans are all familiar by now with Corey Simms.
And not only was she pregnant ... she was pregnant with twins.
As if that wasn't heard enough, months after she gave birth to those two darling baby girls, Gracie and Ali, she began noticing some abnormalities with Ali.
She wasn't hitting the same milestones that her sister was hitting, and there seemed to be problems with her eyes and feet.
After visiting several doctors, they finally had an answer:
Leah learned that her daughter suffered from a degenerative, terminal disease, and one that often brings with it more questions than answers.
Since the form of the condition she has is so rare, there's no real timeline on how slow or fast the disease will progress.
It's simply unimaginable.
But for the most part, Leah has been dealing with the whole tragic thing with grace and strength beyond her years.
As we saw in last night's episode of Teen Mom 2, Messer is always ready and willing to fight for what Ali needs.
During this emotional installment, she spoke at length about Ali with her sister, Victoria, her closest confidant in life.
She explained what had been happening with the poor little girl in a previous episode, which you recall if you watch the show.
On that episode, Ali was rushed to the emergency room because she couldn't breathe in a particularly gut-wrenching scene.
"They did testing on everything, her heart, her lungs," she said. "She does have allergies that are restricting her airways and causing asthma."
In addition to the troubles she'd been having with her breathing, Leah revealed that Ali had also been falling a lot at school.
"She had mentioned to us that she hadn't been eating at school and that she was falling a lot," the 25-year-old said.
"She needs somebody with her, by her side, at all times."
"I'm fighting for Ali," Leah insisted.
"I'm going to do everything that she needs done. We wanted her to be independent, and at the same time things are becoming more progressive."
We've seen both Leah and Corey struggle with that balance - who could forget their unwillingness to get her in her wheelchair like Ali's doctor recommended?
And, at the same time, who could really fault them for struggling with all of this, being so young - and even more fundamentally, human?
After Leah's conversation with her sister, she spoke with some people from Ali's school, and after that, she spoke to Ali herself.
"Whenever you're at lunch and you're going to eat," she told her daughter, "you'll have somebody who'll open your food."
There have been some positive developments lately, despite these monumental challenges. Case in point: Ali learned to ride a bike.
Leah took to Snapchat to share the news, and it was hard to tell if she was even more proud about this feat than Ali herself.
Ali and her twin sister, Aleeah, are both part of a local softball team, which is adorable, and hopefully a sport she can continue.
Previously, Ali quit tumbling (kids' gymnastics) because the strain on her body was too much, but maybe softball will be easier.
While cynics might complain that reality stars are overpaid, it's great that Leah's Teen Mom money can support her daughter.
Far more importantly, Leah has truly been thriving as a single mother for the past year, which has been such a welcome sight.
Because she's been able to work it out with the school to get an aide, which was no easy feat, perhaps things will continue to look up.
In theory, this will assist Ali with whatever she needs help with when Leah can't, and hopefully keep her from falling so much.
It sounds like it'll be a big help for her, but as with everything else, we can't imagine this new development is easy for her mom.
She's come so far since some of her dubious parenting moments (below), and we hate to see her suffer any kind of setbacks.
We know how hard she has tried - and continues to try, day in and day out - to be the best mother and person she can be.
We wish her family only the best. Be strong.