Lenz's Law

Whenever magnetic flux through a loop changes, the loop induces a current. Lenz's law tells you which way that current flows: it creates its own magnetic field that fights the change. If flux through the loop is increasing, the induced current flows so its field points opposite to the change, trying to cancel the increase. If flux is decreasing, the induced current flows so its field adds to what is being lost, trying to prop it up. The current never helps the change along, it always resists it.

Picture a north pole approaching a loop, pointed end first. Flux through the loop, in the direction of the magnet's field, is growing. The loop fights that growth by inducing a current that makes its own north pole on the side facing the magnet, so the two north poles repel each other, pushing back against the approach. Once the magnet passes through and starts moving away, the flux is now shrinking, so the loop reverses its current to make the near face a south pole, pulling the retreating magnet back. The loop always acts like it wants to keep things the way they were.

This direction rule is not an extra law bolted onto electromagnetism, it is conservation of energy showing up as a direction. If the induced current instead reinforced the change, the magnet would accelerate itself faster, flux would grow even more, current would grow more, and so on forever, generating energy from nothing. Opposing the change is the only option that lets the work done against that opposing force be the energy source for the induced current, which is exactly why dropping a magnet through a copper pipe costs energy and slows the fall.