I find it very difficult to find meaning in a large portion of the jobs available today. Most workers are just another cog in the wheel. The system is so large that one cannot directly appreciate the effects of their work, or even know whether they are positive at all.

This contrasts with say, a subsistance farmer who produces food for their family and lives in a small community where every product of their labor has a known and appreciable impact. In that case, the equivalent goal of "changing the world" is "helping the community", which is much more attainable.