“Advice is a dangerous gift, even from the wise to the wise, and all courses may run ill.” -J. R. R. Tolkien

I’m pretty harsh on formal mentorship programs. Maybe, too harsh. During two public presentations last year, I called for the startup world to completely “nix our B-grade mentoring programs,” driving the point home with a photo of a nuclear explosion. I was speaking to an audience of civic leaders and entrepreneurial organization operators. Naturally, some took offense.

Related: Three Steps to Finding a Business Mentor

It’s not that I hate mentors. It’s simply that I despise poor mentorship that wastes a startup’s limited resources.

What constitutes quality mentorship is situationally dependent but I’ve pulled together some ideal characteristics based on my experiences co-founding two companies, LockerDome and GlobalHack.

1. The best mentoring relationships form organically. You cannot force a great mentorship relationship any more than you can force a romantic one. There are a handful of individuals whom I trust to provide high quality feedback for LockerDome. These relationships formed naturally by doing business together, not through a formal mentoring program.

2. Valuable mentors have endured the wild ride of a startup. Avoid the mid-level corporate lifer who recently retired and wants to give back. While well-intentioned, this individual doesn’t have the slightest clue what it takes to win in the startup world.

3. Valuable mentors are domain experts. Beyond someone who understands startups, you need someone who deeply understands your market, or at least a specific piece of it. Disagree? Walk up to a stranger on the street and ask him for feedback on the most pressing professional issue you are facing right now. The odds of his advice translating into recognized value for your specific market are near zero.

Related: Why Mentoring Programs Work

4. Valuable mentors challenge you intellectually. Initial ideas almost always suck, even for world-class entrepreneurs. Effective mentors consistently challenge your assumptions and pull forward a better strategy in the process.

5. Valuable mentors have skin in the game. Family aside, those who will help you the most have the most to gain. This is okay. Embrace it.

6. Valuable mentors will answer your phone call at midnight. Your top 10 priorities almost never match up with someone else’s. The best mentors understand this and consciously make your startup’s needs their priority, even if that means taking your call at midnight.

7. Valuable mentors will spend their reputation points. As a budding entrepreneur, you likely have zero credibility. In ideal mentorship relationships, you’ll earn credibility by osmosis, assuming your mentors are willing to put their name on the line for you and your startup.

8. Valuable mentors are humble. Mentors who “know everything” will push you to imitate their previous wins. Do that and fail. Markets change quickly, and so do solutions. Work with mentors who are cognizant of inevitable change and understand that the best solutions are yet to be invented.

Related: 4 Ingredients for Successful Mentoring Relationships