Strengths are our trump cards.
We already have an edge over them.
They make us start ahead of everyone else.

Weaknesses are our jacks.

We will have to work more than everyone else to even be at par.

Then why is it that people are told to work on their weaknesses and not on their strengths?

Working on our strengths gives us a competitive advantage.
Working on our weaknesses doesn’t offer that; every bit is a struggle. 

Strengths increase on the principle of compounding; so do our weaknesses.

Which one would you choose then?