I think its how you approach life. Are you a glass half full or a glass half empty sort of person?
If you are a glass half empty, you look at the negatives in a situation, and you wont' always follow up/take opportunities.
If you're half glass full, taking the next steps is more instinctive. You are also more likely to take chances, because you feel there is more of a chance of a positive outcome than a negative one.
You can, to an extent, retrain yourself here. Whenever you see the negatives of the situation, deliberately find an equal number of positives about it.
EG
You're alone, don't have a partner - You can make decisions yourself, and don't need to take others into consideration.
You're in a really crappy job - it's worth the risk of changing jobs, it's unlikely that any subsequent job will be as bad.
You are stuck renting and can't buy - you aren't tied to the house, and have the freedom to take up opportunities that require a physical move.
ETC.
After awhile it becomes easier to see the positives in the situation.