Explain why the percentage yield of a reaction is almost always less than 100%, referring to at least two distinct reasons.

1. The reaction may be reversible or may not go to completion, so not all of the limiting reagent is converted into the desired product.
2. Side reactions or competing reactions can consume some of the reactants, producing by‑products instead of the target product.
3. During practical work the product can be lost in steps such as transferring, filtering or purifying, so the amount collected is less than the amount formed.
4. The theoretical yield is calculated assuming 100 % conversion of the limiting reagent, but real experimental conditions rarely achieve this ideal, so the actual yield is always lower.