The more of our attention that's directed to self control, the less energy we have available for deliberate thought. A triumph of self control is followed by a state called ego depletion. We instinctively avoid effort and seek relaxation.
For me, the way to avoid the sloppy thinking that can occur during ego depletion is to plan for some time to bounce back. Don't expect that you can develop this massive will-power muscle that never needs to rest. Just as body builders rest their muscles, we should give our will power a brief vacation. If we plan ahead we can allow for safe, healthy rest and avoid exposure to risky, exciting temptations like drinking too much or spending too much.