Most of us think we have tight hamstrings. 
But here is a little something about a hamstring stretch.   We sort of have a tendency to accidentally cheat and stretch our back in addition to our hamstrings. And sometimes we are even stretching the back and barely getting to the hamstrings.  If you have long arms or a long torso it’s a little easier to get to your toes.  If you have long legs and shorter arms it’s going to be harder.  So the reach to the toes, while an easy standard, can be a bit deceptive.  If I only stretch my hamstrings as far as they can go without curling forward in my back, I can’t touch my toes.
Look at the two pictures above.   In one I’m touching the floor, but that reach all comes from the movement in my back.  My knees are even pretty bent and I’m not getting much of a stretch in my hamstrings.  In the second, I’m letting my spine curl forward so that you can see the difference, but I’m  stretching just my hamstrings without curling forward in the spine and as you can see I can’t reach the floor, but I’m honestly hitting my hamstrings.