There are many reasons why your sink may become blocked. Some of the most common causes include:

• Food waste: Small bits of food can accumulate in the drain and form a blockage over time.
• Grease: Grease and oil can also build up in the drain over time and cause a blockage.
• Foreign objects: Items like hair, soap, and other debris can also get stuck in the drain and cause a blockage.
• Pipe damage: In some cases, the pipes themselves may be damaged or deteriorating, which can lead to blockages and other plumbing issues.

Regardless of the cause, the result is the same - a blocked sink that does not drain properly. This can be frustrating and unsanitary, which is why it's important to address the issue as soon as possible.