Why does 0.1 + 0.2 !== 0.3 in JavaScript, what are safe integer limits, and how do you handle money calculations and 64-bit IDs correctly with or without BigInt?

Imagine you have a pizza and you want to share it with friends. Sometimes you can't cut it into exactly equal pieces because the knife isn't perfect. Computers have a similar problem with some numbers like 0.1 and 0.2 – they can't store them perfectly, so adding them gives a tiny error. For very large numbers or money, we use special tools like BigInt or count in cents to avoid mistakes.