Leanonme, it's an interesting idea in your comment. Rational fears versus irrational fears... definitely worth some more thought...
Is it irrational fear or rational fear if, to use your example, you almost drown and subsequently are afraid of water?
The answer is: it depends. It depends on a number of variables. Let's take a couple of situations.
Let's say I'm a terrible swimmer- I never took lessons and I'm 45 years old and I haven't spent much time around water. I go spend the summer at a lake, and on a calm, beautiful summer day with no wind, no storms, no rain, I'm walking along the shore and I trip and stumble into the water. I almost drown but someone pulls me out just in time.
Ok, now let's take another situation: I'm a fabulous swimmer. I'm 45 years old and have been swimming my entire life- in pretty much anything I can find that's filled with water- lakes, pools, oceans, rivers... I'm as comfortable in the water as a human being can be. And its been demonstrated that I'm very strong in the water. One day I"m swimming around in a lake when suddenly I get a horrible foot cramp. I've never had a foot cramp in my life. It's brutal and I find I can't swim to shore. I almost drown but someone pulls me out just in time.
Based on what you just read, you might expect both Me's to be afraid of the water. Seems pretty reasonable that might happen. I mean, both Me's almost drown.
But we have to look at evidence. Based on the evidence, the first Me probably ought to be wary (if not actually afraid) of the water, and it seems reasonable that that Me would be more afraid of water than I was before I almost drown. Being wary,even a bit afraid, of the water is pretty rational for the first Me. (The antidote, by the way, is for me to learn to swim, post haste! Then I wouldn't have to be afraid)
Based on evidence, the second Me shouldn't necessarily be afraid, long term at least, of the water. I might feel traumatized by my cramp experience, but as I recover from the shock and trauma I should return to a baseline relationship with the water (something close to how I felt about it before my cramp). It's possible I could develop a long-standing aversion and fear of the water from that cramp experience, but based on 45 years of terrific experience with myself in the water and the fact that I'm not prone to cramps ever (in or out of the water), what happened was a truly random occurrence. In this situation, if I become very afraid of the water long term, it is an irrational fear- and I really need to work to overcome it because I seriously don't need to be afraid at that level.
So, as with so many things in life: it depends. There are so many variables in life. It's really not possible to make huge generalizations about many things. Sometimes we can- for instance, I think it's safe to say that we human beings should be afraid to jump off a 1000 foot cliff with no parachute, or to dive off a huge waterfall with an innertube around us.
For our work here, what's important is to continually assess our fears, to continually evaluate which fear/s are useful to us and which are impeding/restricting/oppressing/isolating for us. Come to think of it, the distinction between which fears are rational and which are irrational may not be very important- I think we can focus solely on which fears are helpful to us in some way and which ones are a burden and in the way of our progress on ourselves.