For disjoint events A and B, P(A or B)=P(A)+P(B). This is called the addition rule for disjoint events and it generalizes to more events as long as they are all disjoint.

But something is bothering me. What if A is getting heads on a coin flip, and B is getting a 2 on a die roll, C is getting a heart from drawing a card, etc. Are these not disjoint events?

I'm worried that their probabilities will soon sum to be larger than 1 (once I add enough disjoint events).

I'm sure I'm misunderstanding something here.