Opportunistic relationships ...

Opportunistic relationships can hardly be kept constant. The acquaintance of honorable people, even at a distance, does not add flowers in times of warmth and does not change its leaves in times of cold: it continues unfading through the four seasons, becomes increasingly stable as it passes through ease and danger.
 Zhuge Liang

Quotes from the same author

To overcome the intelligent by folly is contrary to the natural order of things; to overcome the foolish by intelligence is in accord with the natural order. To overcome the intelligent by intelligence, however, is a matter of opportunity.
 Zhuge Liang