Now where was I? Ah, yes...
Probably one of the most important things that I learnt from the Commandos is when to switch off. When we were not required to do our thing, we were absolute sloths ( I remember being almost two hours ahead of schedule for a LRRP deployment once - we stopped in the middle of a pile of dense vegetation, laid down a groundsheet and had a few games of blackjack

). More importantly, we learned never to take unnecessary risks - there would be enough time for risk-taking when the action started.
Admittedly, one risk I took that did not pay off was upon enlistment. I was not a particularly enthusiastic enlistee, and going into the vocational interview, I had a rather stern-looking sergeant ask me, "So, do you want to go into Commandos?". Hoping to show him an attitude that he would disapprove of, I asked him if I had a choice and when he said no, I said, "So what the f*** are you asking me for?". I only found out to my chagrin over the next two and a half years that this was exactly the attitude they were looking for.

Once again dragging myself back to the topic, I will try to address your question of how one comes up with a formula to determine what constitutes calculated risks and what constitutes recklessness.
I think that there are two key differences between risk-taking and recklessness. First, there is the amount of preparation involved. I had no real problem with parachuting because the ground training over two weeks more than made sure we knew the drill and that we checked and double-checked everything. I would be leery of taking a civilian course where the training is covered over the space of a few hours, and where the safety procedures and preparation are, in my opinion at least, inadequate.
The other difference lies in the reason for taking the risk. If there is no reason to take a risk, it does become something of an indulgence. Coming back to Lee's reference to motor sports, the best comeback I can provide to that is to quote three-time Formula 1 world champion Sir Jack Brabham: "I never drive any faster than it takes to win a race.". If you already comfortably leading a race, why push the car so hard that you could end up breaking something and losing the race? On the other hand, if you are lagging behind, you may as well push it and see what happens.
There is a third factor which is something of an interaction between the first two - how much of a risk do you take? The masochist in me loves being in a tight corner, because I can then play it like I have nothing to lose because, well, I have nothing to lose. However, if the situation is comfortable, I tend to avoid shifting the pieces that are already in place - there is no point in wrecking things when I have no need to. To take a risk for the simple sake of it, to get an adrenaline rush, is the opposite end of the scale to "kiasuism"; one approach is as mindless as the other, and both equally lack function.
To tie all of this back to the topic of Remaking Singapore, the problem here is that in Singaporean society, you are expected to not rock the boat - yes sir, no sir, three bags full is the way to go, and independent thought tends to get you marked as a loose cannon on deck. Obnoxious, recalcitrant gits like yours truly generally persist on doing things their own way, but speaking from experience, that does not make life easy for them in Singapore. When they decide that they have had enough and find greener pastures, where their ability to come up with fresh ideas is encouraged, the government labels them quitters. The sad reality is that Singapore is set up to drive away the people best equipped to take the country into the league into which its economy has grown.
On the other hand, we would not be well served by the knee jerk reaction of tying to go to the other end of the scale. That is like plunging a freezing man into boiling water. Certainly, Singaporeans need to be less timid than they are presently, but going back to the equation I cited above, if one were to consider taking a risk, a few questions need to be asked:
1. What stands to be lost if the risk was not taken?
2. What stands to be lost if the risk is taken?
3. How do 1 and 2 weigh up against each other?
4. What proportion of the risk is controllable?
5. What backup measures are there should things not go according to plan?
If the loss is greater when the risk is not taken, and if there are measures already in place to control the situation if things go wrong, by all means go ahead and take the risk. But if there is no point to it, i.e. the answer to 1 is of too low a value, taking the risk would not be the smartest thing to do.
In the situation against the Guardsmen, the recommended course of action in training, if you remember your BMT, would have been either to execute an ambush drill or to fall back in leapfrogging pairs. Because we were outnumbered almost three to one, either course of action would not have had good results for us - in the case of falling back in pairs, we would have effectively been outnumbered five to one. My calculation at the time was that they saw four of us and could not know how many had gone behind the bush ahead of us. From my experiences with Guardsmen (this was my third exercise against them), I expected them to know the drill as well as I did, which meant that doing the tried and tested was something they would likely have been ready for. Again from my experience, the drawback of the Guardsmen was that they rarely deviated from the drill, and I was prepared to take the risk that the Guards' leader would not think as I did. Upon these considerations, I decided to propose this plan to my team, and it worked. It therefore fit the definition of a calculated risk.
A true calculated risk will most likely not match the average person's definition of a risk. The philosophy behind taking a calculated risk is to ensure that the cards are stacked firmly in your favour. Gather as much knowledge of the situation as you can and work out the process so clearly that you can see it happening. Fortune does not so much favour the bold as it does the bold and prepared. A calculated risk is not a question of going, "If I do this, then this will happen, and then this will happen.". Instead, it would be more like "If I do this, these two things might happen. In case of the first event, I can do this, and in case of the second event, I can do that", and so on and so forth, following a branching structure that covers all possible contingencies.
In the case of parachuting, the sequence would be, "If I look up and see a fully open canopy, everything is fine and I can prepare for a landing. However, if I look up and see a partially open canopy, I cover my reserve, pull the ripcord, grab the reserve canopy and throw it out in front of me as far as I can so that it does not get tangled in the main canopy. On the other hand, if I see no canopy at all, I just pull the ripcord. If nothing works, I grab my ankles, pull my legs up to my chest and kiss my precious ass goodbye.".

Well, you get the idea - cover all contingencies before you decide to do something where the outcome is not given. That is a calculated risk.