The purpose of life is to be defeated by greater and greater things.

Rainer Maria Rilke (1875-1963) German poet
“The Beholder [Der Schauende]”, The Book of Images [Buch der Bilder], Second Book, Part 2 (1902) (paraphrase)

This looks to be a paraphrase from a couplet in the poem (also known as "The Man Watching"):

Sein Wachstum ist: der Teifbesiegte
von immer Größerem zu sein.
[Source]

Which translates variously as:

His growth is: to be the deeply defeated
by ever greater things.
[tr. Snow (1991)]

This is how he grows: by being defeated, decisively,
by constantly greater beings.
[tr. Bly]

His growth is this: to be defeated
by ever greater forces.
[tr. Barrows and Macy]