system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What is stoicism?
gpt
Stoicism is a way of approaching living with the aim of having a positive and tranquil life. It originated in ancient Rome with a philosopher named Seneca, who started a school to teach his approach to life, called Stoicism. 

The basic idea in stoicism is to seek out a tranquil and positive way of living by training oneself to appreciate the things one has. This training takes several forms, when people think of stoicism they often think of putting up with misfortune without complaint, or deliberately seeking out hardship. 

A simple example: Imagine your favourite toy, let's say it's a ball. Now imagine that your brother borrows your ball and loses it. This might make you sad and angry but if you think about it, there are plenty of ways for you to play without having a ball; you could run around in the park, or learn how to do cartwheels! The ball isn't really so important after all! Now because we were imagining this, you still actually have your ball - this is great because you haven't actually lost anything but hopefully have a new appreciation for your ball and how great it is to play with, but you also know that, should worst come to worst, you'll be ok without your ball and you'll still be able to have fun. 

So a stoic is calm and ok when bad things happen to her, she knows that she'll be fine because she's learned how well she can cope in rough situations as she has imagined (and sometimes put herself) in bad situations as practice so she really appreciates all the important things she does have. 

Hopefully, if the practice is successful, a stoic enjoys all moments fully: genuinely appreciating all good fortunes, and weathering bad fortunes with a calm joy and lack of regret.