It's one of the few priceless gifts one human being can give to another - blood.
This life-saving gift is one factor Susan Couch, the sole survivor of the 2001 Mt Wellington RSA killings, thanks for ensuring she's still here almost 15 years later.
"Beaten with the butt of a shotgun and left to bleed to death through head wounds and various other injuries, I lost 80 per cent of my blood," she said. "If I had not received the blood I wouldn't be here."
Ms Couch, a single mother aged 38 at the time of the attack, was left with a brain injury and partial paralysis.
Three others at the RSA that December day - William Absolum, Mary Hobson, and Wayne Johnson - died at the hands of William Bell, a disgruntled ex-employee who was out on probation after serving time for aggravated robbery.
Paramedics feared for Ms Couch's life because of her severe blood loss.
But thanks to the donated blood products from some "kind souls" - seven red blood cell units and seven plasma units, a total of just over six litres of blood - she pulled through.
For today's World Blood Donor Day Ms Couch thanked her donors and encouraged others to do the same. "All I can say to those who helped save my life is 'thank you'. Your generosity of spirit and time helped save my life."
While her traumatic brain injury meant she couldn't pay the favour forward, she encouraged others who could to donate.
"One thing I've learned is that it's great to receive, but when you are able to give you get a lot out of it too.
"You get to feel good about yourself and know that you've saved a life - someone's grandparent, mum, dad, sister, brother, child, partner, friend ... is still alive thanks to the kindness and generosity of a stranger who just took some time out of their busy day and donated blood.
"When you donate blood you are saving a life - that's priceless."
Asuka Burge of the NZ Blood Service said donating blood was a selfless act.
Last year 110,000 Kiwis gave more than 160,000 units of blood, helping to save the lives of more than 42,000 compatriots.
This year the service has launched a new mobile app to help donors find a time and place to donate - and tell them when their blood has helped save a life.
World Blood Donor Day
• Today, Tuesday June 14.
• 110,000 thank yous to all our blood donors.
• More than 160,000 units donated.
• New app launch for Android and iPhone available for download.
• #WBDDNZ #nzblood
• To find out how to donate go to: www.nzblood.co.nz