If that's how diving works, lapin, then that's also exactly how climbing works.
You and your partner must trust each other with your lives. If you've ever been on a dive with someone you don't know well or you're not 100% comfortable, you know how it can play with your nerves.
It's the same in climbing.
zippi is wise to treat belaying as just as serious as climbing, because a good belayer makes ALL the difference. after a while, you can learn exactly how to shift around to accommodate various situations.
And catching falls becomes instinct, especially because many falls happen so quickly they are over before you really register what is happening - or, in outdoor situations, teh belayer may not always be able to see his/her partner, but can feel just the slightest adjustment in the rope or when the climber stops.
I instructed beginning climbing for about 3 years, and making people new to the sport as comfortable as possible is paramount to their having a positive, fun experience.
When you climb with someone who's a great belayer, you can actually FEEL the trust and strength coming up the line and it frees you to relax and think and enjoy the experience.