Whenever you have a doubt, surrender the doubt and faith both at the feet of the master. You see, the master is the one who gives you the faith and he is the same person who gives you the doubt. When you are stuck with doubt, tell the master mentally, ‘Master, it is you who gave my faith in you, it is also you who gave me doubts about you. I am surrendering both at your feet. I don’t want to play this game. I have suffered enough with this game. Please take care.’
When you surrender both doubt and faith at the feet of the master, you will see something called trust happens in you, which is neither doubt nor faith. It is the courage to experiment with the truth.

A Zen master was bringing up a small boy from a young age to be his successor.

This little boy had a very deep, loving connection with the master but he was a very naughty boy. He would try to behave in the same way as the master. He would try to imitate and make fun of the master, standing behind him. The master had a habit of always holding his thumb up whenever he wanted to emphasize a particular point. This boy also would stand behind the master and do the same thing!

One day the master got annoyed and just took the knife he was carrying and cut off the boy’s thumb. Understand: the story says very beautifully that the trust and feeling of connection was so deep, the boy did not even think once for a moment that something wrong was done to him. The disciple felt very clearly that if the master does something, it must be good for him.

The story says that this deep trust even during the intense pain enlightened him at that moment.

Understand two important things here.

First thing, that much of connection and trust over the master existed in the boy.

Second thing, the disciple was willing to go through any suffering, pain and any kind of tapas or penance. Penance is being ready to work on the technique at any cost since enlightenment is the first priority. Of course, this technique is for the people for whom enlightenment has become their first priority.

source: Living Enlightenment