The principle of indifference is a fancy way of saying that if we don't have any reason to believe one thing is more likely than another, we should assume they are all equally likely.
Imagine you are playing a game and you need to choose a color, but you don't know which one is the best. Red, blue, green, yellow, and pink are all available. You don't have any reason to think that one is better than the others, so you might as well just pick one at random. This is the principle of indifference in action.
Another example is if you have a bag with 10 marbles in it, and you don't know how many of them are blue or red. You also don't have any reason to think that one color is more likely than the other, so you might assume that there are an equal number of each.
The principle of indifference is especially useful in situations where we don't have enough information to make a clear decision. It helps us avoid making assumptions that could be inaccurate or biased.