Full Idea
As long as a cleavage exists between the particular and the common interest, as long, therefore, as activity is not voluntarily, but naturally divided, man's own deed becomes an alien power opposed to him, which enslaves him.
Gist of Idea
If the common interest imposes on the individual, his actions become alienated and enslaving
Source
K Marx / F Engels (The German Ideology [1846], §1.A)
Book Reference
Marx,K./Engels,F.: 'The German Ideology', ed/tr. Arthur,C.J. [Lawrence and Wishart 1985], p.54
A Reaction
An isolated individual could feel 'alienated' doing menial tasks for themselves when they yearned to get on with their poetry. Alienation is not all-or-nothing. Compare working for a good employer with working for Nazi conquerors.