In reality, the stars are in constant motion. Great distances make the amount of motion small on a human lifetime. Apparent angular motion of nearby stars with respect to more distant stars. These reflect the true motion of the stars relative to the Sun through space.
Proper motions are Cumulative .
It takes many centuries for the effect to build up. It takes many millennia for the constellations to noticeably change shape. In all, it took 2000 years for the motions to become apparent to naked eye observers. Due to the proper motions of the stars that make up the familiar constellation, its shape slowly changes over time. It takes many thousands of years, however, for the effects to be visible to the naked eye.