One important part of 'unintended consequences' is that we get side benefits from our noble efforts.
Recently, I heard a success story about a woman who smoked cigarettes and who was struggling with health and also having a hard time financially. She used public transportation, and was tired of being harassed on her daily commute. So she decided and she began to quit smoking. Her health improved, and it turned out that with the money she saved she was able to buy a car. The improved health was an expected outcome, but the car, that's a great unintended positive consequence; and that's serendipity.
Serendipity sometimes happens while pursuing goals. Serendipity can create several opportunities: