Spend the first few months building your aerobic base. During this phase gradually add volume, stay consistent, learn when to fuel your body during your rides and runs, and have an average heart rate of Zone 1 or 2.

Triathlon training is a mental game as well, generally distance and management. I would wake up at 4:30am and spend an hour or two training. During the work out I'd stay relaxed and maintain a blank mind. Sometimes I focus on one sound such as my footsteps during a run or my breathing during a ride. Acknowledge everything that come and let it pass by. It's meditating. Each new training day gives me the opportunity to practice this mentality. Come race day or even life at work and school my mental state is at ease after all the training I've done. Could be a neurobiological thing.

Yes, some people die. Their heart goes haywire in an open water swim during the competition, heat stroke from run, blood clot dislodged, etc. Hell, one time, I thought I was going to die when I jumped out of the pool after an hour swim and sprinted off to transition for a 30 minute run. My heart fluttered like crazy and I went lethargic. I had to simmer down after learning more about heart rate zone training, what doctors are for and why you should have them by your side as an athlete. But yeah, you probably can decrease risk of death by getting medical check ups and mimicking race day, such as doing a weekly group swim in open water to get a feel of what's hitting your face or pulling you, and having brick sessions.

I'm only a year in, there are still some things I have to learn more about as well such as urine. I wondered why athletes squirt water to their crotch and legs on their ride in Kona '19, and how many athletes would urinate during the open water swim. It fucked me up thinking about this because I've always preferred to be the last in the pack of swim. =/

Do not rush yourself. Love your heart 2020. Scar tissue in heart is no buenos.