Question

why it is said that the water cycle has no begning or end

Answer 1

Because evaporation and condensation takes place regularly

Answer 2

Because the water in the Earth never gets over. The water in the Earth keeps evaporating and condensing. The sun does not go anywhere, so it evaporates  as water. As we keep going higher, the temperature decreases, so the water vapor condenses and forms water as rain

Hope this helps