system
Given the following post, respond as if you're commenting on Reddit:
human
What exactly is a 401K, how does it work, and why is it a good idea?
gpt
ELY5:

When you go to work and make money you have to share some of that money with Uncle Sam.

A 401k is a special bank where the money you put into it you don't have to share that money with Uncle Sam. But you have to wait until your 60 to spend that money. If you spend it before you turn 60 then you have to share some of what you spent with Uncle Sam. Also Uncle Sam will not let you put more than $16k per year in this special bank.

Some nice jobs will put as much money in your 401k bank as you put into it.