While easy jobs have their own perils -- like boredom, and not preparing you for your next gig -- a hard job can be downright scary.

Coming to work and not knowing what you're doing, or knowing that the work will be back-breaking or otherwise very difficult, can shake anyone's confidence. Jobs can be hard for a lot of reasons, but even the hardest can teach us lessons beyond "boy, I want an easier job."

Of course, every job has its challenges, but the hardest jobs we've ever had consistently put us to the test. Below are the lessons learned by three Motley Fool contributors from the hardest jobs they have ever held.

A man with an angry face yells at another man.

There are a lot of reasons why a job can be hard. Image source: Getty Images.

You can't do everything

Selena Maranjian: Many years ago, for a few years, I was a high-school history teacher in a public school in a small city. (I trained as a teacher in an even more urban public high school.) The job offered some great rewards, such as knowing I was imparting important information and helping young minds develop.

It also offered a lot of frustration. Some students came from very difficult family situations, and that made it hard for them to learn. I used to think that if you gave me billions of dollars, I would still not be able to fix all the things that were awry in schools.

As the new teacher, I was seemingly assigned the courses that more senior teachers didn't want. I had five classes to teach each day, and four of them were different from each other. That meant I had a lot of preparation to do each night and on weekends.

Even more challenging, many of my students weren't quite at the level they should have been by the time they entered my classroom. Many were very poor readers and writers -- not to mention poor spellers. That presented a vexing problem: Do I teach them about the Civil War, as expected, or work on their reading and writing, which might be more important overall?

Well, I focused mainly on teaching them history, as that was my job. I learned that there's often more one could do in a job than can realistically be done. Choosing which battles to fight was an important skill I had to develop.

I did try to engage my students in whatever we were doing, to help foster an openness to learning that I hoped would carry over to their other subjects. I couldn't improve the family situations for troubled kids, but I could be a sympathetic soul they encountered every day. The bottom line, I learned, is that you can make a difference in a tough job even if you can't do everything that needs to be done.

Inexperience is not an excuse

Maurie Backman: The summer before my senior year of college, I landed a great opportunity at a big-name investment firm. My role was to support senior associates and financial analysts, many of whom worked 90 hours or more per week on a regular basis.

I knew going into the job that the hours would be tough, and the routine would be grueling, but I figured I could stick it out for the summer, earn a decent chunk of cash, and have something impressive to put on my resume.

What I wasn't prepared for, however, was the sheer amount of responsibility I was given from the start. Though I was pretty much still a kid, I was suddenly on the hook for research, data, and presentations that would ultimately impact multimillion-dollar deals.

In other words, this was serious work, and if I messed up, the consequences would be significant. That's why that summer, I made it my business to ask questions as needed and always get my facts straight, even if it meant annoying people who were pressed for time; to work till all hours of the night on numerous occasions; and to acknowledge some of my own weaknesses.

That summer stint taught me that just because my experience was minimal didn't mean I wasn't held to a certain standard. Thankfully, I stepped up, and was reasonably successful despite the fact that I really was in over my head.

You're not good at everything

Daniel B. Kline: In general I'm a pretty quick study. I've had a lot of jobs over the years, running the gamut from newspaper editor to retail-store manager, from nonprofit public-relations person to full-time freelance writer. Nearly every time I've been able to learn on the job and become skilled at it fairly quickly.

That was true even in my early career when I did everything from answering phones to working at a coat check. Being able to do a lot of things made me confident, and confidence led to arrogance, which in turn led to failure at one short-term job.

One summer, after school let out but before my job at summer camp started, I was doing odd jobs for my family's ladder and scaffolding business. I helped customers, answered the phones, did some graphic design, and generally tried to make myself useful. In most things I was competent, perhaps surprisingly so for my age and inexperience.

That changed on the day they made me a delivery driver. I was handed a set of keys to a loaded pickup truck and a clipboard full of orders to drop off. There was a map in the truck, but this was well before phones had GPS.

The trip was supposed to take half the day -- about four or five hours. I was gone for 12 hours and returned shaken, probably crying, and knowing I was not a good delivery driver. I lacked any sense of direction, which has not improved as the years have gone on. Obviously GPS has made getting places easier, but when it fails I'm still very bad at getting places.

This experience taught me that being versatile is not the same as being good at everything. It was a humbling lesson that showed me that yes, I can learn many things, but there are also plenty of jobs best left for other people.

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