There is the comparison of our mind and its similarities with the inner tube of a bicycle tire. When the tire is fully inflated, there is no problem that the bike can get to its destination, as long as the person is still riding. However, if there are holes in the tire, the air inside starts to leak and, as more air escapes, the bicycle gets harder and harder to ride. This makes the journey for the rider significantly harder and may force him to give up entirely.
The holes in the tube resemble the worries and doubt that we create in our minds. The more we cloud our vision with these disbeliefs, the harder it is for us to get to our final destination.
Mitch's Blog 