Firstly, you may not be the target of the ban itself.
We ban usernames, email addresses and IP addresses. While usernames and email addresses are a per-person identifier, IP addresses are not unique to a person.
Network Address Translation (NAT)
Because there are more people than available IPv4 addresses, some internet providers route users through a single public IP address. That public IP address is what we see, and what can be banned.
Dynamic Host Configuration Protocol (DHCP)
Most internet providers have a pool of IP addresses that are shared between users. This is known as DHCP. You may find yourself in a situation where an IP address was banned whilst in use by person A, and due to the nature of DHCP that address is now in use on your connection.
If you've broken the site rules, you will be banned. Such rules include (but are not limited to):
Sock puppetting (having more than one account per person)
Posting inappropriate content
Abusing other members
Some infractions, such as sock puppetting, come with immediate bans. Other infractions accrue warning points, and upon reaching a 100% warning level you will be automatically banned.
Some bans are permanent and some expire after a given time period.