Around 2 P.M. on April 7 Beauregard decided that his army had done all they could. He realized that continuing the fight would only risk the possibility of his army routing from the battlefield so he ordered a retreat from the field.
Beauregard could have decided to stick it out as long as possible. If the Confederates had continued to hold their ground they probably would have been destroyed. Two more brigades of Buell's army had just arrived on the battlefield and were moving towards the front. The longer Beauregard stayed the more he risked the destruction of his army without much possibility of achieving a great victory.
The risks far outweighed any possible rewards so it is wise that Beauregard decided to retreat. This qualifies as a critical decision because if he had stayed the Confederate army would have probably dissolved.