In gaming, trigger discipline is when one holds his/her gunfire while hiding upon seeing an enemy player walk by him/her in order to see if there are more enemies following the first player/catch the enemy off guard. It requires incredible patience and self control to not open fire on the first enemy you see since there could be more behind the first enemy walking in hence the discipline part of the term.

When you eat dirt for the first time and leave your family to build a shack in the woods