Without God all things are permitted. - Fyodor Dostoyevsky

To think too much is a disease.

...I believe that you are sincere and good at heart. If you do not attain happiness, always remember that you are on the right road, and try not to leave it. Above all, avoid falsehood, every kind of falsehood, especially falseness to yourself. Watch over your own deceitfulness and look into it every hour, every minute. Avoid being scornful, both to others and to yourself. What seems to you bad within you will grow purer from the very fact of your observing it in yourself. Avoid fear, too, though fear is only the consequence of every sort of falsehood. Never be frightened at your own faint-heartedness in attaining love.

Above all, don't lie to yourself. The man who lies to himself and listens to his own lie comes to a point that he cannot distinguish the truth within him, or around him, and so loses all respect for himself and for others. And having no respect he ceases to love.