What derails the mind on its way to Enlightenment?
If you unduly react to trivial circumstances, you derail your ability to think clearly.
If you let negative passions like greed, avarice and jealousy occupy your mind, you derail your ability to think clearly.
If you subsume changing external circumstances, you derail your ability to think clearly.
It is the mind that is trained not to be disturbed by trivial things and circumstances is the mind that can achieve enlightenment.
Remember, the mind should be the master, and should not be influenced by lesser things.