This has been one of my favorite poems since I first read it in high school.

When I was one-and-twenty
    I heard a wise man say,
‘Give crowns and pounds and guineas
    But not your heart away;
Give pearls away and rubies
    But keep your fancy free.’
But I was one-and-twenty,
    No use to talk to me.

When I was one-and-twenty
    I heard him say again,
‘The heart out of the bosom
    Was never given in vain;
‘Tis paid with sighs a plenty
    And sold for endless rue.’
And I am two-and-twenty,
    And oh, ’tis true, ’tis true.

A Shropshire Lad: XIII – A.E. Housman, 1896