A mind directed entirely by its own reasoning will never be sure of anything. As good as the mind is at finding solutions and answers, it is even better at finding questions and doubts.

We were given minds so that we would reason and question. But we were also given Torah and its sages, so that our reason would have a faithful guide.

Ponder the truths the sages teach.
Take them apart, examine them with a critical eye, and then put them back together.
Your mind and heart will resonate with those truths,
until all your deeds are guided by a voice that has no second thoughts.