My patients ask me plenty of questions. They are trying to understand their medical circumstances, and I want to offer the best of explanations. Sometimes, in order to simplify my explanations, I call upon an analogy, and to be more specific, I compare my patients to a car.

Why a car and not a giraffe, apples, or oranges? Because cars break down as often as people get sick. Because cars need fixing and people need healing. Because both cars and people are complex structures the working of which is both miraculous and difficult to understand.

Here are several of my car analogies:

Ms. A., 65, tells me, “I am going to the bathroom every 20 minutes, I feel an urge to go, and I can’t hold it.” In response to my questions, she admits that she drinks “a ton of fluids,” including plenty of coffee, and some soda too. I suggest that she should cut down her caffeine consumption because caffeine acts like a bladder stimulant–and may worsen the symptoms of overactive bladder. She responds in disbelief, “I have been drinking like this my entire life. If caffeine is the culprit, why is my bladder acting up now and hasn’t given me any problems before?”

“Your body is like a car,” I tell Ms. A. “You can drive a new car fast and furiously, but if you kept driving it at the same speed and ferocity when your car gets older, it would rattle, fall apart, and, heck, your wheels might fall off. In a similar way, when you become older, your bladder ages as well, and you can no longer “drive” it the way you had been doing, overloading it with fluids and caffeine.”

On another day, I see Mr. S., who was recently diagnosed with a low-grade prostate cancer and who seeks a second opinion regarding the course he should take. “If it’s cancer,” he asks me, “shouldn’t you take out my prostate, or at least treat me with radiation?”

Mr. S. is 74. He had been a heavy smoker and isn’t in the best of health. He is a heavy-set man who appears short of breath and walks with a cane. Just a few weeks ago, he tells me, he was diagnosed with a failing heart, and his diabetes hasn’t been well controlled for a while.

I tell Mr. S., “Your body is like an old car. And when you have an old car, it starts collecting problems: the body starts to show rust, the engine burns oil, and the transmission doesn’t switch gears. You keep driving it around, it gets you places, you fix this part and replace another, but the problems keep piling up, competing among themselves as to which of them will cause your car to finally stop.”

Now that I have mentioned cars, I have my patient’s full attention. I tell him that we need to take his age into account, and also to consider his other serious medical conditions. I say, “your medical conditions, including your prostate cancer, are competing among themselves as to which will kill you first. And in this scenario, the diagnosis of low-grade prostate cancer isn’t the end of the world. In other words, you’re more likely to die with prostate cancer than from it, and when the time to die comes, hopefully years from now, you are more likely to die of old age than of prostate cancer.”

On another day, Ms. K. asks me: “my doctor told me that I should drink plenty of water, and at the same time, he ordered me to take diuretics in order to get rid of excessive fluids in my body. Wouldn’t it be easier if I just drank much less fluids?”

I tried to explain to Ms. K. the relationship between heart failure and leg swelling. I touched on the subject of bodily fluid distribution and fluid balance. I used simple terms that I thought would clarify the subject but Ms. K. was still unsure and seemed even more confused.

So I called, once more, upon my car-body analogy. “My body is like a car,” I told her. “So I am driving my car along the highway and all goes well. The engine is humming peacefully, the transmission is shifting smoothly, my GPS shows the road ahead. And I can ask, ‘How is my car’s engine, transmission, or GPS working?’ And I admit that I know nothing about the mysterious ways in which my car is working, and yet, I’m going places and meet old friends and make new acquaintances.”

Reading Ms. K.’s facial expression, I dare to conclude that she might have found solace in the fact that her body still miraculously works even as she can’t fully understand how. But then, she asks, “But, doc, if my body is like a car, why can’t I trade it in for a newer, better model?”

EDITOR’S NOTE: Dr. Shahar Madjar is a urologist at Aspirus and the author of “Is Life Too Long? Essays about Life, Death and Other Trivial Matters.”