varies; Make a self-control roll whenever it would be wise to deviate from your goal. If you fail, you continue to pursue your Obsession, regardless of the consequences.
You must make a self-control roll any time the GM feels you show an unreasonable degree of caution. If you fail, you must go ahead as though you were able to handle the situation!
You may fight – you may even start fights – but you may only use deadly force on a foe that is attempting to do you serious harm. Capture is not “serious harm” unless you are already under penalty of death or have a Code of Honor that would require suicide if captured. You never intentionally do anything that causes, or even threatens to cause, injury to the uninvolved – particularly if they are “ordinary folks.”