Hamilton's Rule: You are Selfish

As per Hamilton's rule,

rB>C

where, r is the relationship between the two individuals involved, B is the one you would sacrifice and C is the one you want to save.

So basically what is its significance?
It states that our genes work in a very selfish manner. It tends to take decisions which are most favorable for its retention and preserving its own identity.

Let's understand it by an example.

Say You went on a trip with your daughter and 3 of your nieces (your sister's 3 daughters). And suddenly you met an accident. Somehow you saved yourself but now got stuck in a critical condition.
And that condition is: You can either save your own daughter or 3 of your nieces. So whom would you save?
Well, as per Hamilton's rule,
Your relation with your daughter is 50% (the other 50% is from your wife). You also have a 50% relation with your sister (say only one sibling). and your sister has a 50% relation with each of her daughters so your relation with her daughters (your nieces) would be 50% multiplied by 50% which is 25%.
Now, applying Hamilton's rule-
You want to save your daughter so C = 1 multiplied by the relation = 1 x 0.5 =0.5
You would sacrifice 3 nieces so B=3
and r= 0.25
rB=3 x 0.25 = 0.75

So since rB > C, you would rather save 3 of your nieces and sacrifice your daughter. 
If you had only once niece in the same case then, rB = 0.25 x 1 =0.25
so rB < C and in this case you would save your daughter and sacrifice your niece. 
So basically, even if you sacrifice your daughter to save 3 of your nieces, you are selfish as per Hamilton's rule.
 Your genes want to preserve its own identity and hence make you take such a decision.