For deterrence I would say prison or any other punishment will only work if the person you're trying to deter has more to lose than to gain by their activities. This depends on the circumstances and a person living relatively comfortable probably wouldn't want to risk going to prison, but the less comfortable a person is living the less they have to lose and more risk they have to take to change their condition. In some environments, young people are getting killed, or are homeless, etc, and in those environments going to prison isn't worse than the alternatives from a rational perspective. Most will think it's better to be alive in prison than to be dead, and a lot of people will think being in prison is less of a punishment than being homeless with no where to go.