Plastic is cheap, light and strong, which is why it is used for bottles, bags and toys. The same qualities create a problem: plastic does not rot away, and a bottle thrown on the ground may remain for hundreds of years. Much of it ends up in rivers and then in the sea, where it harms fish, turtles and birds that mistake it for food. Recycling is one answer. Used plastic can be collected, cleaned, melted and made into new products such as clothes or park benches. However, recycling is not perfect. Not all plastic can be reused, and the process needs energy. For this reason, many experts say that the best approach is to use less plastic in the first place. Carrying a cloth bag to the shop and a refillable water bottle are small steps that anyone can take.

Question: Why does the writer say that recycling is not perfect?