Everyone knows that experience, when it comes to diving, reduces the risk of accidents and injury; but all experience is not created equally.
Training experience does provide us with a great place to start. No one would want to experience first hand why it is important to not hold your breath or to equalize your ears. This is where learning from others through classes and additional training comes in handy. 
Practice also provides us with experience beyond what can be learned in a classroom. It allows us to take what we have learned in the classroom and use it to reinforce our learning in a controlled environment. Practice is especially important when it comes to emergency procedures. When an emergency arises, we fall back on what we have learned and practiced, so be sure to practice these skills often. 
Diving provides the ultimate experience that is very difficult, if not impossible, to get while receiving instruction. It provides a real life application for all the things we have learned. It also allows us to become familiar with what diving is actually like. However, remember that quality and variety is more important than quantity. A diver who has done 1,000 dives all on shallow tropical reefs in relatively calm water is going to be less experienced than a person who has logged 200 dives in a variety of environments and conditions. 

While diving is a great form of exercise, most of us don't dive regularly enough to use it to stay fit. Staying fit throughout the year also has benefits in diving such as being able to move around more comfortably in the water and needing less weight to dive.
Here are some common fitness anecdotes that can be helpful if they are facts but are sometimes just something someone made up. Here is what DAN has to say on these 7 common fitness myths.

1. Drinking cold water during or after exercise is bad for you- FICTION
Cold water has been shown to be more readily be absorbed by the body making it a great way to quickly rehydrate the body. It can also help with body-temperature regulation. If you are cold after diving drink warmer water, if you feel overheated drink cooler water.

2. A short workout provides no benefits- FICTION
Time can be the enemy when trying to maintain a healthy and fit lifestyle. Any amount of time spent exercising is beneficial. Every step counts and 3-10 minute workouts can be just as good or better than 1 30 minute workout

3. If you are working out you need a sports drink- FICTION
Sports drinks can be over-sweetened and can actually cause many people to actually gain weight as the sports drinks often add unnecessary calories to their diet. Drinking these might make your exercise null and void. Gatorade has 200 calories so it would take about 2 miles of running to burn this off. Water is just as effective in providing re-hydration without the extra calories.

4. Sit-ups and crunches eliminate belly fat- FICTION
While these exercises do firm up muscles in the area, there is no evidence that these exercises and muscle development and fat cell loss. The only sure way to lose weight is to make sure you are burning more calories than you are taking in.

5. Weight gain can be caused by lack of sleep- FACT
Lack of sleep creates a hormone imbalance. This imbalance causes your body to think it is hungry and needs to get energy from food rather than stored fat. Often people choose high-carb and/or high sugar snacks when they are tired which also contributes to weight gain.

6. You have to stay in the "fat burning" zone to burn fat- FICTION
Many exercise machines have low levels of exertion that are labeled as the "fat burning" zone and high exertion levels as the "cardio" zone. It is true that you do burn a higher percentage of fat in the "fat burning" zone but the actual loss through calorie expenditure is minimal as the exertion is minimal. 90% of only 30 calories is not as much as 25% of 200 calories. The key here is to spend more calories than you take in and not to worry about percentages of what is burned for weight loss.

7. Exercise improves brain function- FACT
Exercise boosts blood flow to the brain and increases brain activity. It also has been shown to help with building new brain cells and making new connections between brain cells. These things can increase your intelligence and speed up brain processing.