Imagine the problem is picking a path against an unexplored desolate desert wasteland. One guide says that he's the fastest. Runs not walks, at a fork in the way always picks a path within 5 seconds. They promise you that they are the fastest guide out there by a factor of two.

You decide on a second opinion, and find an old wizened guide who says they always walk not run, never picks a path more quickly than 5 minutes, and promises you that no matter what sales pitch the other guide gives they can get you across the desert in half the time and half the risk to your life.

Both can't be true. Who do you believe and why?