Developing Error Opportunities

I'm never able to catch myself making a coding mistake before it happens.  The funny part, for me anyway, is after the fact when I discover what the issue really was — it was a trivial error.  And the pattern I followed leading up to the error was avoidable.  How could I not have seen this coming, I sometimes question.  Is the answer that only in hindsight are these types of things obvious in an activity as complex as writing software?  That may be the answer.  But even still, I think it is both interesting and worthwhile to think about this type of software development pattern.  What makes us predictably and repeatedly successful, and what makes us unpredictably and repeatedly error-prone?