[4] Punishment may be used to deter potential future offenders by showing them what the consequences of breaking the societal rules may be and encourage conformity to the norms within the society.
[8] This is part of the reason why, historically, some punishments have been particularly brutal in order to have a greater deterrent effect - notable examples of this include the executions of Balthasar Gérard or Guy Fawkes.
As humans can learn vicariously through observing other people punishment can make for a highly useful tool to deter undesirable behaviour and encourage following social norms.
[9][10] Solitary confinement is a controversial punishment that some claim to be ineffective at preventing undesirable behaviour in prisoners in addition to being inhuman.
[11] Additionally it has been well documented that long-term exposure to solitary confinement (or similar conditions) can lead to a variety of mental health issues including self-harming, depression, anger and hypersensitivity which severely impacts the prisoners ability to reintegrate into society once their sentence is complete.