Source

The rate of return we earn.
This is impossible to say anything about on beforehand. So it is basically a waste of time to fantasize about.

Whether we’re building on a strong foundation.
It will be less emotions and fear involved in investing if there is a strong foundation in the form of control of the personal economy. Limiting debt and being sensible.

How much we save.
Quote: “Invest $200 a month for 20 years at 10.0 percent and it will grow to $153,000. You could improve that to $216,000 by either (1) increasing your rate of return to 12.5 percent annually, or (2) adding a mere $1 to the amount you invest each month. Which do you think would be easier?”

How much we lose to taxes.
Be sure to make full use of tax-advantaged accounts like IRAs and 401(k)s.

How long we save.
Compounding over long periods of time. Start investing early.

How much we invest in stocks versus bonds.
Stocks give a higher return in the long term, but stocks will give some unpleasant movements in the short term.