Left to right is how I read, and it usually gives me an answer, just apparently the wrong one.
Accepted answer
Because the same written expression would mean different things to different people, and math needs one answer.
`2 + 3 × 4` is 20 left to right, but 14 with order of operations. The convention exists so a formula written in one place means the same thing everywhere.
The order — **PEMDAS** — is grouped, which is where most mistakes come from:
1. **P**arentheses
2. **E**xponents
3. **M**ultiplication and **D**ivision — *same tier*, left to right
4. **A**ddition and **S**ubtraction — *same tier*, left to right
Multiplication does **not** outrank division. In `8 ÷ 4 × 2`, you go left to right within the tier: `2 × 2 = 4`, not `8 ÷ 8 = 1`. Same for addition and subtraction. Reading PEMDAS as four strict levels instead of two-plus-two is the classic trap.