Just in time for Labor Day, a reader critical of my views on immigration sends along some career advice. "You really need to find another line of work," he wrote. "You are not worth a (expletive) at what you are doing now. I hear they need strawberry pickers."

This guy owes an apology - to strawberry pickers.

He thinks he's insulting me, but he's really insulting agricultural workers. I don't know whether a farmworker could do my job. But, coming from a family of farmworkers, I'm absolutely sure I could never do his.

When George W. Bush used to say that Mexican immigrants did "jobs Americans won't do," a lot of his countrymen got their pride hurt and insisted that this wasn't true.

Nonsense. Of course it is. The U.S. economy is full of dangerous, dirty or distasteful jobs that Americans have outgrown. These are the jobs that grandma and grandpa did - tarring roofs, milking cows, cleaning horse stalls, picking apples, shelling crabs, etc.

But were they to attempt any of it, most members of Generation Y wouldn't last an hour. As a member of Generation X, I'm part of a heartier crew. So I can say that, in my case, I wouldn't last 90 minutes.

Thus, when someone tells me to pick strawberries, I feel like that person might as well have told me to become an astronaut and fly to the moon. Anyone who thinks it's easy picking enough strawberries to support a family has obviously never picked strawberries - or, for that matter, anything else.

I remember seeing an interview with a strawberry farmer who said that, in 25 years of growing the crop, he had never had a single U.S. citizen approach him for a job working in his fields.

It's just as well. What we often forget is there is an art form to this kind of work. There are people, like my grandparents, who resembled machines as they methodically plowed through those fields. They worked hard, but they also worked smart and learned tricks along the way to become more efficient.

Farmworkers have a simple way of inspiring their children to stay in school. It's called take your kids to work day. It did the trick for my parents, who toiled in the fields alongside their siblings in 100-degree temperatures and dreamed of one day simply working in an air-conditioned office.

An uncle told me a story about how, when he was a teenager, he worked his heart out in the fields. At day's end, my grandfather told him that he had better hit the books because, if he had to survive out there, he wouldn't last long. About 40 years later, my uncle's son - who had a chiseled physique, spent many hours in the gym and once tried out for a professional football team - ventured into the fields to see what it was like. As my cousin tells it, he couldn't keep up with the Mexican workers and, after a while, was just trying not to pass out.

Recently, I heard a similar story from a reader who said he was a Marine. He and a buddy were home on leave and decided to go into the fields to make extra money. They were in excellent shape, he said. And yet, after a couple of hours, they were sucking wind and couldn't wait to get back to their base.

We should remember stories like these when we hear politicians talk about whether U.S. immigration policy should be to let in the "skilled" or "unskilled." Americans tend to think that skilled means educated and trained. But what it really means is having the ability to do something that someone else can't or won't do.

Such a skill is worthy of respect. During Labor Day weekend, let's acknowledge this truth.