I'm not sure what you think an average salary is. If you think an average engineer can save $50k cash per year out of his/her net income, you're way above the average I had in mind.
Let's assume an average salary of $120k per year gross. That's about $6k per month net for a single person who takes the standard deduction, assuming no 401k contributions. That's a net income of $72k per year. If that engineer saves $50k, that leaves only $12k for everything else. Saving $100k in two years on that salary, which I think is pretty close to the average, is just not doable.
EDIT: Should have been $22k left over, not $12k. Still not enough to live on considering the cost of rent.