I've done 17 dives and have never had to abort a dive. Yet.
I have seen people abort dives:
1. One guy was a blood donor and gave blood, and decided to go on a dive the next day. It was a beach dive, 3 foot waves, low tide, so you had to really kick out there. We'll he couldn't make it not even half way, had to stop and swim back, and ended up going to the hospital! We actually went online to research the reason, we'll we already know that red cells carry oxygen, so the guy's hemoglobin must have dropped after the donation. He was an older man I wanna say maybe 40s or 50s.
2.Same day, same dive, it started off somewhat calm on the beach dive, and then got rough and one girl just didn't dive she aborted. It was too rough to swim out. If she would have gone in at 8am it would have been fine but just that quick... 930 those waves and the wind picked up.
I definitely learned the importance of maintaining a level of fitness as a diver, because I ran out of air and we were still past the pier and had to kick back.it can get veery strenuous..
Also, Just come prepared, and they say to start packing at least 3? Days before a dive (if you have your own gear) , that way if you have to areplace missing or damaged parts like a fin strap, or O-ring before your dive, you gave time to do it before u go.