Markovnikov's Rule

"The Rich Get Richer"

This video explains what this means when an addition reaction occurs to an alkene where the two carbons involved in the double bond are not the same:

Two products are formed, a major product and a minor product. As the names suggest, more of the major product is formed, but there is actually a mixture of both products when addition occurs to this type of alkene.

Here is another example:

http://www.chemguide.co.uk/organicprops/alkenes/propenehcl.gif