Most prisoners will have to be accepted back into the community at some stage, the chief inspector of criminal justice in Northern Ireland warned.
Brendan McGuigan said it was as difficult as ever for those who had served sentences to find jobs upon release.
Good rehabilitation measures were critical to help prepare inmates for their freedom, he added.
He said: “We still, as a society, have concerns about serious offending and whether people can be accepted back into the community but the truth about it is they have to be, because everyone sentenced to imprisonment will be released at some stage.
“The work inside the prison becomes more critical then.
“It is about ensuring that these people don’t re-offend.”
Research showed increased age helped stop people from lapsing back into old behaviour.
Around four out of 10 ex-prisoners committed another crime within a year, Justice Department statistics for 2015/16 showed, more likely within the first month of release from custody.
The highest rates of recidivism were among those who committed burglaries or robberies.
The proportion re-offending appeared higher for those whose first brush with criminal justice came when aged in their early teens.
The official report said it appeared to decline with increased age.
Mr McGuigan said: “Although we are sentencing 24 or 25-year-olds, some are behaving like 10 or 11-year-olds.
“It is not until they get into a meaningful relationship and there is a bit of pressure put on and actually they then start to wise up.
“Then you will get the career criminals who unfortunately have worked out for themselves that they are prepared to take a risk because the rewards for them are greater.
“Then there are the really violent and dangerous people, where we have the indeterminate and extended sentences which are there to try and manage them in that environment.
“There are some people in Maghaberry that might never see the light of day.”
Maghaberry in Co Antrim is Northern Ireland’s high-security prison for men and houses a mixture of convicted prisoners and those who are yet to be tried.
Mr McGuigan added: “The reality is most of them are going to be released so it becomes critically important that the work you do with them there is actually addressing their offending behaviours and preparing them for release.”
Many companies at the application stage, or at interview, ask if the applicant has a criminal conviction.
The shoe repairer and key cutter Timpson has been notable for its employment of ex-convicts.
Some years ago a branch in Belfast attracted adverse newspaper comment over the policy.
The charity NIACRO has helped support ex-prisoners to develop their employability skills while providing intensive mentoring.
It has also dealt with referrals of those released from prison but under threat of violence or exclusion from their communities.