A big part of self-discipline comes from social pressure. This is how people in the military can become very disciplined, particularly in special forces. They don’t want to hold their team back, so they have to do their best.
Worried you won't meet your goal? According to research, you'll be more likely to succeed if you make specific plans to implement it.
People have an easier time starting toward a goal than finishing it, but a shift in attention can make all the difference in reaching the finish line.