Or is a well organised, robust, structured code base that you can fly through and make changes at will?
A second one uses a little custom framework. We have more test cases for this one so we can mash through it w/o much concern. The total codebase is less than 200k lines (excluding framework). We can move fast but this makes little money
A third has 4 devs, uses a common well known framework and each dev writes one test case a week (our test process is gamified). Makes good money and we can move pretty quick but have a methodical Work, Test, Beta, Live process too.
I still tiptoe though, because in my experience over-confidence is a recipe for disaster.
I go for the well structured approach, but you don't always have the luxury of time unfortunately.