Whether and when to terminate an employee is one of the most difficult decisions leaders ever make. Most of us agonize over these decisions and even once we've made our choice, we spend a lot of time wondering if we did the right thing.

While it's not always possible to know for sure, asking yourself a few simple questions can help you make the right choice. Just as important, they can stop you from second-guessing yourself later on.

Andrew Filev, CEO of the project management software company Wrike, has had his share of experience with hiring and firing as his company grew from less than a dozen to 120 employees today. Here are the questions he recommends when facing a tough fire/don't fire decision:

1. If this employee applied for a job today, knowing everything you now do, would you hire this person?

If your answer is yes, or even maybe, then it probably makes sense to retain that employee. He or she is clearly bringing some value to your organization.

2. If this employee were to resign, how would you feel?

If your reaction is relief, you should probably part ways with that employee. This person isn't contributing anything of value. Or even if he or she is, the negatives are clearly outweighing the positives.

3. How will firing this person affect the company culture?

You should always consider how firing someone will affect the rest of the team, particularly in a start-up. For Filev, this issue came into play in Wrike's early days when he was faced with a software engineer who consistently underperformed--but not for lack of trying. Filev hesitated mightily to fire the engineer. At the time, Wrike was a very small company where everyone worked 12-hour days and team spirit was essential.

So Filev explained to the engineer that customers were complaining about his work despite many attempts to improve. Then he asked, "What are your thoughts?" The engineer cared about the company and knew that things weren't working out. He asked for time to find another job and left as soon as he did.

4. Why did things go wrong?

"Let's say you have 20 sales reps and 19 of them are meeting their quotas, and you have one who isn't meeting expectations even after guidance and training. This is the time to let that person go. They might be a great salesperson but not the right fit for your company," Filev says.

On the other hand, if you're selling a new product or entering a new market, and your rep is trying hard but just can't make quota, the problem may not be the salesperson. So before you go any further, determine whether the issue is with the employee or with the job itself.

5. Did you provide timely guidance?

"When a bad situation starts to unfold, it helps if you give early feedback," Filev says. "In the case of a sales rep who doesn't make quota, that rep should know that if it happens again the following month he or she will be let go. It should never be a surprise."

Whatever else happens, you owe it to all your employees, strong and weak, to provide feedback that will help them do their jobs better. And that feedback should come early enough to give them a chance to improve before things go south.

6. Did I make a bad hire?

"It's not just about one person, you have to learn for next time," Filev says. "Was it the wrong person for the role? Was the timing wrong? What should you have done differently?"

It's important to find answers to these questions, he says, since firing someone is such a tough thing to do. "The pain you feel when you let someone go should drive some learning."