It's a legitimate concern. When I first started diving, I was afraid of sharks. Not afraid to dive, but afraid of actually encountering one (or more). When I saw how they react to people (snorkelers and folks splashing on the surface), I lost my fear. I had about 10 - 15 dives (I was on a live aboard - The Impossible Dream - in the Bahamas where I was certified) and everyone was maxed out. This was in the days before computers and no one had any time left on the tables. The boat was anchored, I was standing on the bow watching the water. Most of the folks were playing on rafts and/or snorkeling at the stern (approximately 60 feet away). They were doing a bunch of splashing. Looking out in front of the boat, I saw something moving towards the boat, just under the surface. As it got closer, I saw it was a large (8 - 10 ft) shark (I never did ID it) moving slowly and gracefully straight at the folks off the stern. When it was right beside the boat (right under me), a spasm when through it's entire body. He then made a 180° turn and swam away very quickly. That was the day I lost my fear of sharks.
From that time, I looked for sharks. I saw my first (while in the water) on my 49th dive. Shark sighings are rare (in most locations) and wonderful (almost always). In the over 20 years I've been an active diver, I've been lucky enough to see sharks many times. I'm often reminded of their fabulous grace and beauty. They are usually difficult to approach, but you can sometimes entice them to approach you. I'm philosophically against the concept of feedings. Sometimes, they'll swim beside you for a short time, allowing you the opportunity to admire them. If you hang motionless, they will sometimes come in close to investigate before running away. Once on a safety stop, I was able to get a 6 ft Caribbean Reef to approach to within about 3 feet before it turned and swam rapidly away. That was a moment to be treasured, one I'm glad I was able to experience.
Then there are the rogues. Sometimes, they don't act like you expect. There are times they get aggressive. If interested, you can read about my one such experience in the Florida Conchs forum (Running with the Bulls....). If you encounter an aggressive shark, don't try to run away. Swim slowly to the exit point and get out of the water. Make a strong confident impression (don't swim with your hands, have neutral buoyancy). Make noise, shout, growl, etc. If the shark charges you, swim right at it. Make it think you are the apex predator. This type of behavior is extremely rare, so don't let it keep you from diving.
Yes, I've also been struck by lightning.