When learning to play bridge, it's easy to mistake exceeding one's contract as a "victory". With this mindset, players often err on the side of underbidding instead of trying to appropriately bid based on the cards they've been dealt. This results in more points "above the line", but less progress towards winning the rubber - the actual goal.
If you're bidding to earn the maximum number of points "below the line", you should fail to make your contract as often as you exceed it. The bidding process is an estimation exercise; some hands have unexpected synergies and others just don't work well together. Good bidding results in you making your contract most of the time and going over or under by one trick the rest of the time.
As in life, if you're never failing, you're not aiming high enough.