Brian Willington, 33, stabbed Martin Latham eight times in the chest outside Asda, in Wolverhampton Road in Heath Town, on September 6 last year.
The 41-year-old grandfather, who later died in hospital from his injuries, had been trying to act as a peacemaker when a fight broke out at the car park.
Willington, who denied two charges, was convicted of murder and possessing a bladed article at Wolverhampton Crown Court last week after a trial.
Prosecutor Michael Duck QC said the evidence was "plain" and the defendant had taken the knife to the scene which was used in committing the murder.
The court heard how eight "substantial" wounds were inflicted to Mr Latham aimed at the upper-chest area which were delivered as the victim tried to "evade the attack".
Mr Duck QC said the attack, which was "blow after blow", had plainly demonstrated an intention to kill, rather than cause serious injury, and said there had been no warning for Mr Latham to "walk away" prior to the confrontation.
He asked the court: "If you intend to cause somebody harm and only that, why go to the fourth, fifth, sixth, seventh and eighth blows whilst pursuing a man backing away from you?"
A victim impact statement, read out in court by the victim's sister on behalf of the family, described the tragic loss of Mr Latham – with his mother having suffered "enormously".
He was described as an "idolised" member of the family who was loved by his friends and was called as a "loveable rogue" by all those who knew him. Mr Latham had endeavoured to change his life around – having plans to move closer to his family, a judge heard.
Wolverhampton Crown Court was told the attack was "cowardly, evil and unforgivable" with the family left asking one question: "Why our Martin? And still we're asking this very question. I know in my heart we will never receive an honest answer."
His sister told the court Mr Latham wanted "better for himself" and was "robbed" of the opportunity, adding: "For each of us it's been a struggle to get up each day and continue life without Martin.
"We will never forget Martin and the pain we all feel will never subside."
Mr Gregory Bull, defending Willington, said his client had shown "genuine remorse" and had penned a letter to the court ahead of his sentencing – and offered condolences to the family.
Mr Bull said: "My client accepts what he did was quite unforgivable, there was no need for it and he knows no words of mine can soften the blow his family have received by reason of his actions."
Wolverhampton Crown Court was told the defendant had been an alcoholic by the age of 15, he had a rough childhood through no fault of his own, and was a man with "enormous problems" and has suffered from a number of psychotic disorders.
Judge Michael Chambers QC, sentencing, said: "Mr Latham died as a result of a senseless, repeated stabbing attack by you. It happened because you were carrying a knife, a sharp kitchen knife. Tragically, this is another fatal stabbing that occurred because the assailant had a knife available to use. So when an altercation occurred, the assailant – you in this case – used the knife, stabbing – in this case an unarmed man – some eight times.
Judge Chambers QC added he was satisfied the defendant knowingly smoked the drug mamba jointly with a group, which contained Mr Latham, prior to the altercation and the knife wounds were delivered with "significant" force, with one of the stab wounds penetrating the heart.
Willington was sentenced to life imprisonment with a minimum term of 22 years for murder, which was reduced to 21 years and 120 days taking into account the 245 days the defendant had spent on remand.
The 33-year-old, of Hawkley Close, Moseley, Wolverhampton, was handed no separate penalty for possession of a bladed article during the hearing at Wolverhampton Crown Court on Thursday.