Last week, I was talking to an entrepreneur, and one of the things that stood out was the passion in his voice. You could tell he was fired up and committed to building a business with a strong sense of customer empathy.

When talking to entrepreneurs, I always enjoy asking questions like: Why did you start this business? Why is now the right time to create this company? What makes you uniquely suited to succeed? While these are important questions, a key nuance is the passion exuded by the entrepreneur. Does he really care? Does he truly want to make this happen? What sacrifices is he willing to make?

The challenge with discussing passion is that it can be subjective. Different personality styles express passion in different ways. Some people get excited, talking fast and with high energy. Others become serious, showing a deep conviction. While passion comes in different forms, it’s ultimately one of those things you recognize when you see it.

One final note is about the intersection of entrepreneurs searching for a great idea versus being passionate about that idea. This can be a tough balance. Great ideas are hard to find, and while some entrepreneurs are passionate about anything and everything, others struggle to get excited even when they find a strong idea. For many, that lack of excitement is a dealbreaker.

From my experience, most things that move society forward, help others, or solve meaningful problems provide a foundation for passion. Of course, it’s ideal to find a need in an area you’re already passionate about, but I wouldn’t limit the search for a great idea to things that are immediately exciting.

The next time you talk to an entrepreneur, listen to his voice. Pay attention to the excitement around the idea. After the conversation, do a mental analysis of his level of passion. Some of the most successful entrepreneurs I know are also the most passionate about their mission.