Unwanted price movement, also known as "price drift" or "market impact," occurs when a large order execution causes the market price to move against the trader's interests, resulting in a worse execution price. This can happen in both directions:

1. *Buy orders*: When a large buy order is executed, it can drive the price up, resulting in a higher execution price than expected.

2. *Sell orders*: When a large sell order is executed, it can drive the price down, resulting in a lower execution price than expected.

Unwanted price movement can lead to:

1. *Slippage*: The difference between the expected and actual execution prices.

2. *Trading losses*: Executing at a worse price than expected can result in immediate trading losses.

3. *Reduced trading performance*: Repeated instances of unwanted price movement can negatively impact overall trading performance and profitability.

To mitigate unwanted price movement, traders use various strategies, such as:

1. *Order fragmentation*: Breaking large orders into smaller pieces to minimize market impact.

2. *Price averaging*: Executing orders at multiple price points to reduce the impact of price movement.

3. *Algorithmic trading*: Using automated strategies to optimize order execution and minimize market impact.

4. *Liquidity provision*: Working with market makers and liquidity providers to access better prices and reduce market impact.