In aerospace engineering, mass is the enemy. To get anywhere in space, you need speed (Delta-v), but to get speed, you need fuel—which adds mass, making it harder to get speed.
This relationship is governed by the famous Tsiolkovsky Rocket Equation:
$$\Delta v = I_{sp} \cdot g_0 \cdot \ln\left(\frac{m_0}{m_f}\right)$$
Where $\Delta v$ is the change in velocity, $I_{sp}$ is specific impulse (efficiency), $m_0$ is initial mass, and $m_f$ is final mass.
Here is a Python function to calculate how