A while back, I used farther in a headline when I should have used further. I did the same thing in the body of the article.

Looked OK to me. Looked OK to spell-check. 

Then I received at least 50 "Um, dude, I hate to be the bearer of bad news ... " emails.

I was glad people pointed out the mistake. (If you ever catch a typo, please tell me.) But I hated the fact I made it.

Just as one misspelled word can get a résumé tossed into the "nope" basket, one wrong word can negatively impact your entire message. (And dent your self-esteem.) 

Here are some grammar and spelling mistakes -- including when to use farther and further -- that spell-check often won't catch:

Affect and Effect

In terms of verbs, affect means to influence: "Impatient executives affected our scheduled implementation date."

Effect means to accomplish something: "The founder effected a sweeping policy change." 

Even so, when to use effect or affect can be tricky. For example, a founder can affect changes by influencing them, or can effect changes by implementing them.

So use effect if you're making something happen, and affect if you have an impact on something someone else tries to make happen.

As for nouns, effect is almost always the right choice: "At 5 p.m., the children quickly gathered their personal effects and rushed out of the building." 

Affect refers to an emotional state; a person in a "blah" mood exhibits a flat affect. So, yeah: Unless you're a psych major, you'll rarely use affect as a noun.

Compliment and Complement

No one ever receives enough praise, so make sure you get this one right.

Compliment means saying something nice. Complement means adding to, enhancing, improving, completing, or bringing close to perfection. 

I compliment your staff.

But your app complements your website. Or if all your positions are filled, you have a full complement of staff. Or I can order an entree with a complementary dessert included in the price. 

If you offer me a free dessert, that's complimentary. And is something I should compliment you for doing.

Ensure and Insure

Most of the time -- especially if you want something to happen -- ensure is the way to go. Ensure means to make sure. Insure is, yep, insurance. (While there are exceptions where insure is correct, the safe move is to use ensure when you will do everything possible to make sure something happens.)

Need to hit a ship date? Take steps to ensure product goes out on time. Of course, you might decide to insure the package, especially if the contents are extremely valuable.

Farther and Further

Use farther when referring to physical distance: "My desk is farther from the copier than yours." 

Further involves a figurative distance: "I don't think I want to take these negotiations any further."

So while Bryson DeChambeau can hit a golf ball farther than just about any other professional golfer, he still works to further his hit-it-far approach.

Infer and Imply

This one is a matter of perspective. If I say you seem tired, my intent may be to imply you aren't working hard. But if I say you look tired, you might infer I don't think you're working hard.  

In short, the communicator impliesor suggests. The person communicated to infers, or reaches a conclusion. 

I might imply volume discounts are possible. You might infer buying in bulk will result in lower unit prices. But for now, it's just supposition. 

Less and Fewer

Use less when referring to items you can't -- or haven't tried to -- count, like "less money" or "less time." Think of less as "not as much."

Use fewer when referring to items you can or have counted, like "fewer hours" or "fewer dollars." Think of fewer as "not as many."

Also apply the "sounds right" test. Even though both are countable, "less inventory" sounds right while "fewer inventory" does not. "Less waste" sounds right and "fewer waste" does not.

But when less and fewer sound interchangeable -- and spell-check doesn't intervene -- use less for "not as much" and fewer for "not as many."

Systematic and Systemic

If you're into processes, procedures, or implementing difficult change, systematic is the way to go: Systematic means arranged or carried out according to a plan, method, or system.

You can take a systematic approach to employee development. You can make a systematic evaluation of your competition. You can systematically work to gradually reduce errors and waste.

Usesystemic if you're referring to an ongoing situation or condition. Lack of diversity could be systemic. Avoiding responsibility and ownership could be a systemic problem.

A lack of employee development opportunities may be systemic -- and may require a systematic approach to change and overcome. 

If you're referring to a pervasive issue, by all means use systemic. (Or just say, "We have a major problem that affects our entire company.")

Then make sure you take a systematic approach to ensure -- not insure -- you overcome the problem. 

You're and Your, It's and Its: the Dreaded Apostrophes

In simple terms, the apostrophe in it's denotes contraction, not ownership. It's doesn't own anything; it's is short for it is. As in, "It's too crowded in here." 

Ownership doesn't involve an apostrophe. If you own a dog, its collar might be red.

Same for you're. It's (see what I did there?) the contraction of you areYour involves ownership. Your house. Your business. Your investors, not you're investors.

And one last thing about apostrophes: Don't toss them in for fun. Words that are plural but don't own anything don't need apostrophes.

I recently saw a sign that read "(John Doe's) Tractors, ATV's, and Mower's."

The tractors didn't own anything. But I doubt the ATVs or mowers did either.