This was all confirmed in my latest copy of "Visual Studio Magazine". An article on debugging says:
First, make a plan and think about the consequences of your changes. Make sure you understand how the code is supposed to work, how it actually works, and how it will work after you make the change. Remember that bugs are caused by not understanding the code. Make sure you understand the situation before you act. Changes to old code are far more likely to introduce new bugs than writing new code is, so think before you make matters worse.Truer words have not been said!