How do I know that God does not want me to do a certain thing?

What Allah desires in terms of sacred law can be known by learning its rulings and referring to people of knowledge, as Allah Almighty said: "So ask the people of the message if you do not know," and as the Prophet, peace and blessings be upon him, said: "Why did they not ask if they did not know? Indeed, the cure for ignorance is asking." As for knowing what Allah desires in terms of divine decree, there is no way to do so, because it is from the unseen. In worldly matters, one can perform Istikhara (prayer for guidance) and do what the soul is comfortable with. The facilitation of a matter is a sign of good in it, and its lack of facilitation is a sign of no good.