Every probability lives between 0 and 1. 0 means impossible, 1 means certain, 0.5 is an even-money coin. You can never get a chance below 0 or above 1 — if your answer does, you've made a slip.
Theoretical
0.50
Experimental
—
Heads / flips
0/0
A fair coin is theoretically 0.50 heads. But flip it just 10 times and you might get 7 heads (0.70) — experimental and theoretical disagree for small samples. Keep flipping and the experimental line creeps back towards 0.50. Small samples are noisy; large samples settle.
Two traps live here: a probability must sit on the 0-to-1 line, and you may only count outcomes when they're equally likely. And experimental only matches theoretical when the sample is big.