The primary reason for the occurrence of ocean tides is the gravitational pull exerted by the Moon and the Sun. The Moon's gravity creates a bulge in the Earth's oceans, leading to high tides in the areas directly beneath it. Conversely, the areas perpendicular to the Moon experience low tides. As the Earth rotates, different regions of the planet experience these changes in tidal levels. The Sun also influences tides, although its effect is less pronounced than that of the Moon. The interplay of these gravitational forces results in the cyclical pattern of tides.