It starts with one

One thing, I don't know why
It doesn't even matter how hard you try
Keep that in mind, I designed this rhyme
To explain in due time, all I know
Time is a valuable thing

Watch it fly by as the pendulum swings
Watch it count down to the end of the day
The clock ticks life away, it's so unreal
Didn't look out below
Watch the time go right out the window