If I'm reading code, I can give 100% of my attention to the logic and details and edge cases, so I'm more likely to pick them up.
While as I'm writing, I'm busy doing all of the stuff that writing code involves, so I'm more distracted and more likely to make mistakes.
This gets proved to me time and time again when I run something for the first time and have to debug it. I look at the offending line, and think -- how could I have made a mistake so obvious that it's immediately apparent? Well, because I was busy/distracted thinking of 20 different things while writing it. But it's immediately obvious when reading it, because it has my full attention now.
If I'm reading code, I can give 100% of my attention to the logic and details and edge cases, so I'm more likely to pick them up.
While as I'm writing, I'm busy doing all of the stuff that writing code involves, so I'm more distracted and more likely to make mistakes.
This gets proved to me time and time again when I run something for the first time and have to debug it. I look at the offending line, and think -- how could I have made a mistake so obvious that it's immediately apparent? Well, because I was busy/distracted thinking of 20 different things while writing it. But it's immediately obvious when reading it, because it has my full attention now.