Mouse that has but one hole is quickly taken

Meaning:

• You should not depend on just one thing because if it fails, you will not have any alternatives. You should always have 'plan B' in reserve.  

Example sentence:

He's a fantastic sportsman and he's doing very well now but unfortunately, he's decided to quit school. But what will he do when he gets older? Mouse that has but one hole is quickly taken.



Questions for you to answer:

1. Can you think of any situations where this idiom/proverb is relevant?
2. Are you the type of person who likes to have more 'holes' in reserve or do you tend to always depend on one thing?
3. On the other hand, what are the dangers of having too many 'holes'?