By default, both tangents on an anchor scale evenly. This keeps the arc of the curve balanced on both sides of the anchor.
You can weight the tangents on an anchor to one side manually to create an uneven arc.
When you move one tangent away from the anchor, the opposite tangent is unaffected.
Alternatively you can select a tangent and select Edit Curves > Bezier Curves > Tangen Options > Uneven Anchor Tangents.
You can even out weighted tangents so they are the same distance from the anchor.
You can also align the tangents to an average of both tangents by selecting the anchor instead of a tangent and performing these steps.
Alternatively you can select a tangent and select Edit Curves > Bezier Curves > Tangen Options > Even Anchor Tangents.