Over the years, I've had hundreds of conversation with people who now love their jobs even though they were formerly miserable at work. Based on those, here are the infallible red flags that signal that you must let go--of your job, your project, or your company.

1. You know that your product is second best.

Unless you're a sociopath, you won't be happy at work if you feel in your gut that your customers are making a mistake every time they buy from you.

2. Your dread of Monday is ruining Sunday.

A little bit of Monday-morning blues is normal, but when that feeling starts rippling into your weekend, your job is starting to ruin your real life.

3. You don't respect the people you're working with.

If you see unethical behavior or persistent stupidity among your peers, staying where you are will damage your self-respect.

4. You don't believe your company strategy.

It may have made sense to you before, but if your strategy doesn't make sense now and there's no way to change it, you're pursuing a lost cause.

5. You sense you're not making a difference.

If you're not actually changing the world for the positive in some way, you're either wasting your time or you're making things worse.

6. You find yourself complaining too much.

Assuming you're not naturally negative, if you notice that you're always grousing about work, it's a good indication it's not the right work for you.

7. You're bored more than you're "in the zone."

When you're doing what you love, the workday whizzes by.  By contrast, if your workday drags on and on, the job you're doing is not the job for you.

8. You know you can't fulfill your potential.

Twenty years ago, a management consultant pointed out that I would never be able to do my best work inside a big firm. He was right. I left and never looked back.