Sometimes, one event can affect the outcome of another.
There are 3 red candies left in a bag of multicolored candies with a total of 20 candies left in it. The probability that you will get a red one when you reach in is: 3/20.
But what are your chances of getting a red one if you reach in again?
There are now 19 candies in the bag, and only two are red.
The probability is 2/19.
Taking the first candy affected the outcome of the next attempt.
The two events are dependent.
Now you know that the probability of a heads-up landing when you flip a coin is 1/2.
What is the probability of getting tails if you flip it again?
It is still 1/2.
The two events do not affect each other. They are independent.