It depends on what you mean by "sideways". Here are a few possible interpretations and why they might be true:

* During launch: Rockets often tilt sideways as they ascend vertically because of the Earth's rotation. This is to help them stay on course and avoid being carried off-target by the Earth's spin. Think of it like throwing a ball - if you want it to go straight up, you need to aim slightly ahead of your target to account for the Earth's movement.

* In space: Once a rocket is in space, it may maneuver sideways to change its trajectory or orbit. This is similar to how a car uses its steering wheel to change direction. Rockets can use their engines to apply thrust in different directions to achieve these changes.

* To achieve a specific orbit: Some rockets may launch sideways to achieve a specific orbit that requires a horizontal component of velocity. For example, launching a satellite into a geostationary orbit requires a sideways velocity to match the Earth's rotation.

It's important to note that rockets generally launch vertically for the following reasons:

* Gravity: It's the most efficient way to escape the Earth's gravitational pull.

* Atmosphere: A vertical launch allows the rocket to minimize the time spent in the atmosphere, reducing drag and maximizing efficiency.

So, while a rocket might sometimes move sideways during its journey, it's not always necessary, and vertical launches are generally the most efficient way to get into space.