The Soviet decision to withdraw from Afghanistan was made in October 1985, several months before Stinger missiles entered Afghanistan in significant quantities in the autumn of 1986. None of the secret Politburo discussions that have since been declassified mentioned the Stingers or any other shift in mujahideen equipment as the reason for the policy change from indefinite occupation to preparations for retreat.
10 myths about Afghanistan |The Guardian
▻http://www.guardian.co.uk/world/2011/sep/27/10-myths-about-afghanistan