They used to say "never" in tennis.
Now it's a staple, and nobody I know misses the arguments with the chair umpire.
I was at the US Open this year, and on the outer courts, they don't have Hawkeye. It was a stark reminder of how difficult it is for humans to get it right every time with world class players and the speed they hit the ball. It added an element of uncertainty that did nothing but detract from the game, both from the players point of view and the crowd as well.
It's coming, as it should be, and all we're doing now is going through the growing pains to get it implemented.