Sacrificing means bidding over the opponents, expecting to fail. You hope that either you will be cheaper than the opposing making (game) contract; or your opponents bid one more and go down.
Players generally over-sacrifice, often committing the crime of taking two bites of the cherry. Sacrificing does not generally pay because if you are left to play (doubled, of course), your bid will only gain if all these factors occur:
Top players hate to make late sacrifices: the opponents have no sensible option other than to double. Advance sacrifices are much better – because now there is a good chance the opponents will bid on (eg 5 ♠ over 5 ♦ ). And now your sacrifice bid can never lose. It will break even if 5 ♠ makes; and gain handsomely when 5 ♠ is one down.
Exercise: Here are three auctions. Give a mark out of ten for the tactical nous of West’s 5 ♦ bid in the following auctions:
|1 ♥||2 ♦||2 ♥|
|3 ♦||4 ♥||Pass||Pass|
|1 ♥||2 ♦||2 ♠|