Hiring is one of the most important responsibilities of any founder. In the early days of a startup, one bad hire can cripple or even sink the company. Based on my 15 years of working with startups, I’ve found there are three things founders must avoid during the hiring process:

1. Hiring too quickly

Pressures like shipping the product on schedule or gaining more traction in the market can tempt you to rush the hiring process, even when you’re not 100% sold on a candidate. In my experience, though, those hires almost never work out, as you’re effectively hiring either a B player or someone who is not the right fit for the role. If you know from the start that your expectations don’t match the applicant’s capabilities, you’re setting them up for failure. It’s important to take your time with hiring—for both parties’ sake.

The key to hiring A players is to look for people who can do the job better than you could do it. If you’re hiring in a domain area that you don’t know about—for example, if your background is in product and you’re trying to fill a sales position—bring in someone with relevant experience to conduct the interview. Yes, this slows down the process, but slow is good when it comes to hiring.

2. Not recognizing bad hires

A common mistake startups make is failing to recognize a bad hire by confusing activity with progress, or experience with expertise. Just because someone is working long hours doesn’t necessarily mean they’re getting things done. Sure, there are many days when you need to work 15-hour days to get the product out or prepare for a launch, but that’s not a healthy or sustainable lifestyle. In my experience, productive people are efficient, and they don’t count the number of hours worked. They count deliverables.

See also: The Dumbest Thing You Can Do in Business

Once you realize an employee is not working out, whether it’s due to lack of productivity or because they are just clocking in and out, you’ve got to have a heart-to-heart with them to level set expectations. Put them on a performance plan, chart out some measurable short-term objectives, or do whatever else you need to in order to discern change in behavior and productivity. Personal issues can severely impact performance, so it’s only fair to have that discussion. But if you don’t see a change in productivity after that, you’ve got to let them go. Fast is good when it comes to firing.

3. Hiring outside of company culture fit

When I interviewed for my first startup job at Wily Technology in 2000, there were 14 people at the company, and I met with pretty much all of them. The interviews weren’t all technical or even related to the job, but the process gave me a great feel for the company, and certainly gave the company a great feel for me. I found out after the fact that the last interview was specifically designed to gauge culture fit. As I reflected on the exhausting day on my flight back home, I was certain that if I had bombed the culture fit interview, I wouldn’t have gotten the job.

People don’t join startups just for the stock options. If their heart isn’t aligned with the company’s mission, values, and culture, not only are they not going to be successful, but the company will suffer greatly. At Wily Technology, we were about 250 people at the time of acquisition, but we tried very hard to only hire people who had a culture fit. And the few who we did hire outside of this fit never really worked out. It’s important to define your company culture, get everyone’s buy-in, and fight hard to only hire those who embody it.

There is a good reason why every successful entrepreneur will tell you that recruiting quickly becomes their highest priority: When your startup only has six to eight employees total, it’s not hard to see how one bad hire could ruin the momentum and sink the company. At the end of the day, the biggest reason for a startup’s success or failure is its people.