I would like to add my 'two cents worth'.
I would say that 50/50 is the figure we use because it's convenient, but the real figure is always going to be infinitesimally greater on one side or the other because of environmental factors such as how the hand was angled, sweat on the hand, how you breathe, coin imperfections, air currents..... Each time you toss the coin the odds would be different, in favour of either heads or tails, so it comes down to the laws of physics, which is why we would never end up with a million tails in a row.
Isn't it true that each throw has 100 per cent chance of being heads, or 100 per cent chance of being tails because the outcome is decided before the coin even leaves the hand?