Some friendships are like chemistry - lots of fireworks, explosions even, and if among opposite genders, perhaps some chemistry..? 

Some are like physics. Lots of difficult problems that make no sense, and lots to do. 

Some are like Accountancy - always about profit and loss. 

Some are like maths - adding and reducing, multiplying and dividing... but somehow, never really adding up to much. 

Very few are real friendships.. just that.. friendships.