I have had a couple of friends attempt to donate blood recently who were turned away because the machines weren’t able to draw from them.
Tubing issues were blamed first.
Eventually, the staff told them they couldn’t donate because the flow was being blocked by clots.
In both arms.
These people are all under the age of 35, by the way. And were under the impression they had no health issues.
I did the same.
It's REALLY hard.
I know of a kid, a YouTuber, who has needed two heart transplants.
He's now in palliative care.
He wouldn't be alive now if no one had donated.
On the other hand, you can't trust the people who harvest.