Creative punishments for a variety of needs.
Penance is defined as:
Voluntary self-punishment inflicted as an outward expression of repentance for having done wrong
Punishments—whether self-inflicted or by others—are a useful tool to promote accountability and getting things done. Punishments should be used more often (when and where appropriate) to help people accomplish their goals. And while this is a motivation/discipline band-aid of sorts (since an external risk is willing the action to get done), it can work, and if it works, what's the difference between doing it of one's own accord?
Punishments must be costly and carried out without any exception (within reason). Cost can be in the form of social status, money, time, physical pain or discomfort, or lost opportunities. It should be prioritized by whatever is most impactful to the person getting punished: if they care about looking good in front of others, then the punishment should make them look terrible; if money is tight, put that on the line, enough that it will be difficult, but not impossible, to live without. Enforcement should be carried out by someone else to ensure no mental gymnastics are done to get out of the consequences that await—find a friend, family member, accountability partner, etc. Like any bet, make sure the conditions of success and failure are rigorously defined to, again, avoid mental gymnastics that somersault one's way out of discomfort.
Some of these are my own (denoted by an asterisk after the name), others are from outside sources (friends, internet, etc).