NEC ECC - How a Contractor gain profit under option A

I have worked in different options in NEC but just had a question that how the contractor will get a profit if they have chosen Option A.  
From my understanding and the terminology of the contract is 'Option A is a priced contract with an activity schedule where the risk of carrying out the work at the agreed prices is largely borne by the contractor.

So the contractor is well aware that he is taking a risk while choosing the contract but wondering how the contractor will make money in this type of contract. Please can you explain. Many thanks. Kishore