Those conditions which flatter hope and attract desire are so constituted that as we approach one we recede from another. There are goods so opposed that we cannot seize both, but by too much prudence may pass between them at too great a distance to reach either.
 Samuel Johnson, The History of Rasselas, Prince of Abissinia (1759). copy citation

Context

“Perhaps there is a time when marriage might unite them—a time neither too early for the father nor too late for the husband. ” “ Every hour, ” answered the Princess, “ confirms my prejudice in favour of the position so often uttered by the mouth of Imlac, that ‘Nature sets her gifts on the right hand and on the left.’ Those conditions which flatter hope and attract desire are so constituted that as we approach one we recede from another. There are goods so opposed that we cannot seize both, but by too much prudence may pass between them at too great a distance to reach either. This is often the fate of long consideration; he does nothing who endeavours to do more than is allowed to humanity. Flatter not yourself with contrarieties of pleasure. Of the blessings set before you make your choice, and be content.” source