if we reduce the period of observation to a single year, we find a wavelike trend with peak in a late summer and a trough in late winter.
if we reduce it to a single week, the waveform narrows to a sharp peak in the weekend.
but over a much shorter period [half an hour], the number of people on the beach remains constant and the trend line is horizontal.
these general trends of accelerating growth, wavelike cycles, or stability are function of the period over which observations are made.