There are tens of trillions of cells in my body and every one of them has about an arm's length of DNA, packed as 23 pairs of chromosomes. Now I know it sounds impossible that molecules several feet long could be packed into the nucleus of a cell too small to see with the eye, but take my word for it, I've done the math, and it fits nicely.
Each strand of DNA is terminated at both ends by a sort of aglet (the little plastic cap on the ends of shoe laces), called a telomere. The telomere insures that the meaningful part of DNA is accurately replicated.
Each time a cell reproduces the telomere gets a bit shorter, and many biologists believe that's one reason we age. All those DNA shoe laces unraveling at the ends.
Now they tell us that the integrity of telomeres is diminished by stress. No surprise there, but I can feel my aglets peeling away even as I write. Just thinking about those diminishing telomeres is stressing me out.