Involved in and a part of life
[A]s things are designed in this world of sentient life there can be no good, no sweetness or pleasure in life, nor peace and contentment and safety, nor happiness and joy, nor any beauty or strength or lustre, nor any bright and shining quality of body or mind, without pain, which is not an accident nor an incident, nor something ancillary to life, but is involved in and a part of life, of its very colour and texture.
from W.H. Hudson's Hampshire Days (p.28).
I've heard many variations on "Life is pain" from the Buddha to The Princess Bride, but never so eloquently stated as this.