Computers store decimal numbers in binary floating-point, and just like 1/3 can't be written exactly in base 10, many simple decimals like 0.1 can't be written exactly in base 2 — it becomes an infinitely repeating binary fraction that gets cut off at some precision. Adding two of these rounded approximations together can leave a tiny leftover error. It's not a bug in any particular language; it's the IEEE 754 standard nearly every language uses, and the fix is usually to compare numbers with a small tolerance instead of ==.