Why we're stuck in Afghanistan

I think this paragraph from this BBC story more or less sums up why we're so bogged down in Afghanistan.

 

"It seems strange to plan and carry out such operations that gain ground, only to pull back straightaway, but British forces say they do not have the troops to completely secure such vast areas - and they never could have."

Forgive my ignorance, but does this not strike you as the sort of situation that's going to result in constant battle without victory or indeed defeat?