The will. Works every time.

We like to lie to ourselves a lot about why we
do things, because often our true purpose isn’t
very nice or noble and doesn’t fit the ideal
image we have of ourselves. You can’t know what
your will is if you lie to yourself. There should
always be at least one person with whom you are
completely open and painfully honest, and that
person should be you. Give yourself permission to
be imperfect, and realize that if what you see
when you look inside isn’t very pretty — well,
that too is your will. Besides, nobody else has
to know your ugly, secret truths if you don’t
want them to — and everybody else has their
horrid little secrets. It’s called being human.
Cut yourself some slack. It goes good on crackers.
...
If you’re going to do something, whether saintly
or despicable, do it right. Step one is to know
what you’re trying to do.

“Do what thou wilst shall be the whole of the
law” means to live on purpose, and doing that
lets you live better than you can if you just
stumble your way through.

The whole essay.