You have a score, starting at, say, 100.
Flip a coin (it is a perfect 50/50 coin),
if you get heads - your score is increased by 80%,
tails - decreased by 50%. Sounds good, right?
Right?
You can also force an outcome, to see what happens
after a certain amount of heads and tails.
The reason why you get below 1, unable to climb back up, SO MUCH, is simple:
so, on average, your score decreases,
even though you "get more from 1 head than lose from 1 tail".
* score is rounded to 4 decimal places
full explaination: https://youtu.be/_FuuYSM7yOo