1) Complexity is very expensive 2) Written code can take a long time to stabilize and is thus expensive to change and maintain 3) Ostensibly orthodox legacy s

1) Complexity is very expensive 2) Written code can take a long time to stabilize and is thus expensive to change and maintain 3) Ostensibly orthodox legacy systems are full of anti-patterns. 4) How easily a small problem can turn into an infinite number of other, small problems, and the intuition required for where to 'draw the line'.