My very first job was digging ditches for the Water Board when I was 16. I had just finished high school and was about to go to uni.

I did it for about three and a half months, putting a sewerage system in Wollongong.

It was quite illuminating because I knew nothing about labouring, I had no idea about the skills involved. I learned how to use a shovel, which is interesting because it’s different to using a spade. You’ve got to use your body in different ways.

I remember one day we laid 50m of sewer pipe in Dapto. We had to dig up the ground by hand, then lay down a bed of sand and then lay the sewer pipe and then the concreter would pour the concrete on top. Then more sand, followed by a layer of dirt. It was very easy ground to dig.

One night I saw a movie called The Young Philadelphians starring Paul Newman, who plays the part of an illegitimate child. He grows up and falls in love with a girl from a wealthy family. There’s a line in it where Newman says to the girl, “Honey, I love you so much I’d even dig ditches for you”.

The next day one of the guys I was working with, I still remember his name – Stan Gifford – asked me if I watched the movie and if I heard Newman’s line about digging ditches. I told I had and then he said, “Let me tell you something, you’re smart and you can do anything you want. Not like me, all I’ll ever do is dig ditches”.

I didn’t appreciate his advice at the time. But I knew both Stan and I respected the skill of ditch digging. I miss it. I had the best waist of my life when I was digging ditches!

My first professional job was as a physicist at a steel works in Wollongong. I was 19 and had just graduated from uni. My job was to measure various aspects of the strength of steel made by BHP. I had to design and build a machine from scratch, which would measure the fatigue life of steel. It was for the construction of the West Gate Bridge in Melbourne.

Imagine you have a paperclip and you bend it out straight and bend it out some other ways. You can probably do that four or five times before it breaks. But if you don’t bend it as much, you can probably do it up to 5000 times. This is like measuring Ultimate Tensile Strength, or UTS, which is testing how much stress a material can withstand before breaking.

My boss wanted me to fake the results of my tests because no matter what I did the metal strength didn’t match with the specifications. He kept asking me to check my figures and so I did, but nothing changed.

When I spoke to my colleagues about it, they told me the boss wanted me to fake the results.

Things got bad between the boss and I, so I resigned.

From that job I learned to have a good combination of self-doubt and self-confidence. The self-doubt was when I went back to check the figures and got my colleagues to check them as well. The self-confidence was when I said, “No, I’m not doing that”.

Ultimately the metal strength had nothing to do with the collapse of the West Gate Bridge.

I was only at that job for a year and a bit. I was 21 and it was tough resigning. Even though one of my mates faked his results, I knew it was the wrong thing to do.

Dr Karl’s latest book, Game of Knowns, discusses why psychopaths make good kings, why the left side of your face is the most attractive, why we drink beer faster when it is served in a curved glass and other quirky scientific theories.