Doubt is essential to your health goals, says Mark Sisson. If you're too sure and get stuck on your beliefs, you end up ignoring the other possibilities that can lead to the real ah-ha moments that help you break through plateaus and reach your goals. So, have a little doubt.

Agnostics are often characterised as ambivalent or wishy-washy fence sitters who refuse to make up their minds. But there's much more to agnosticism than these tired misconceptions, including a stricter adherence to scientific principles than those typically invoked by atheists.