Google will tell you that a sine wave or sinusoidal wave is the most natural representation of how many things in nature change state.In other words things have a tendency to go up and down with monontonous regularity.(The wave that Klopp is doing in the pic is for representational purposes only and is not a sinusoidal wave!)

Liverpool have gotten themselves stuck in a sinusoidal wave.
After the crests of beating Man City and West Ham they then slumped into the trough of losing 1-0 to Nottingham Forest of all teams.
Now they have gone and beaten Rangers 3-0 again in the Champion’s League and so are back on a crest.(Highlights)
We can expect the next trough any day soon