Everyone should be happy if they have a job and if they’re smart, they should hold on to it at all costs, right? Think again.

Even in a lackluster job market there are instances when you should start looking for other opportunities. Whether you are stuck in a dead end role or the thought of going to work is starting to make you sick, it behooves you to begin the job hunt now before the bad situation consumes you.

“Way too many people stay in jobs well past when they should, and like cheese, after a while it starts to stink,” says Julie Bauke, career strategist, president of The Bauke Group, and author of “Stop Peeing on our Shoes: Avoiding the 7 Mistakes that Screw Up your Job Search.” “In my experience, many people, after being let go, can tell you, in retrospect, almost exactly when the worm started to turn, and when they should have taken action to leave. It’s just that we tell ourselves all kinds of stuff that keeps us stuck.”

Change is hard, but it can also be good, which is why it’s important for people to recognize the signs that their job and potentially even their career with their current employer is starting to sour. According to career experts, valid reasons to start looking for better employment include looming layoffs, a business that is underperforming expectations or a situation where you are being excluded from important meetings and assignments.

Lack of job growth, especially if you are doing everything you supposedly need to get promoted and it’s not happening is another good reason to quit. According to Bauke, telltale signs that you have hit a dead end include being left out of discussions and meetings you would normally be a part of, your ideas are routinely ignored and when you ask about career advancement, you don’t receive a clear answer.

But it’s not only those situations where you’re concerned about your next pay check or career advancement that are justifiable reasons to leave. Often the most valid reasons to move on are to preserve your mental health and physical well-being.

“Dreading going to work in the morning or breaking into a sweat on Sunday night is usually a good indication that you are working against your strengths or are in a toxic culture for you,” says Susan Ruhl, a managing partner at OI Partners — Innovative Career Consulting in Denver. “In cases of harassment or just intolerable working conditions, sometimes, it’s not worth it to one’s physical or mental health.”

While it’s important to protect your mental and physical health and to grow in your job, career experts caution that it’s better to find a new job while you are gainfully employed than to quit on a whim and then start the hunt. After all, not only will you be more confident if you have a job to fall back on, but you will also be more desirable to the companies trying to court you. “I rarely recommend quitting without another job,” says Joel Garfinkle, author of “Getting Ahead: Three Steps to Take Your Career to the Next Level.”

If you are employed you won’t get the “why did you leave your job” question nor will you feel needy or insecure, he says. Nobody can predict how long they will be out of work and if the unemployment languishes for months with no unemployment benefits because you chose to quit, you’ll likely become desperate, which employers can spot a mile away.

“Once you start noticing you don’t like the job immediately, evaluate your finances,” says Garfinkle. “Know how much money you have to hold you over and be prepared for the transition. Start looking for a job a few months before you want to leave.”

For many employees that are miserable in their job, they make the mistake of not looking for new work whole heartedly. They may submit a resume here or there, but they fear their boss will get wind of it if they go full court and beat them to the punch by handing them a pink slip. While it’s ok to nibble, once you are ready to go you are going to have to get the word out with your professional networks and that includes on LinkedIn and other social media sites.

“If you don’t really leverage all social mediums out there, you undermine your opportunities,” says Garfinkle. “You want your network to help create opportunities for you.”