求之不得 [- - bù dé]seek but fail to get; all that one could wish for; exceedingly [most] welcome; fail to find a thing after searching for it; just what one (has) wished for; so rare that it is not to be sought:
•¶求之不得的事情 just what one wants
•¶ 这是求之不得的机会。 This is a most welcome opportunity.
•¶求之不得， 不求自来。 Follow love, and it will flee; flee love, and it will follow thee.