Strange combination!

Time for a serious blip, would someone like to explain how the most tested athletes in the world who are tested all the time round the year, for 7 years he never tested positive but now he's a drugs cheat!!! So how exactly does that happen? and even if it's right and he did how can others that have admitted in using drugs be able to throw lance under the bus and get off Scott free themselves! And in other news, gotta love big bang theory! :)